The list below shows how each California county was created and the trail of later additions which stayed in the county. They do not show the trail of territory which is no longer in the county. To obtain that information, look at the information of the individual counties listed under “Territory which at one time was in [this county] is now in [these counties].

Of the original 27 counties, after 1850 only Marin neither added nor lost significant land to another county. Of the 32 California counties created after 1850, only seven counties neither added nor lost significant land to another county. The seven are Alameda, Alpine, Imperial, Madera, Modoc, Orange, and Riverside.

In addition to the substantial territorial changes listed, many small changes were made to boundaries. Several of these small changes were made at the time of the creation of new counties.

Original county boundaries often followed geographic features such as mountain ridges. In the middle of the last half of the nineteenth century many of these boundaries were changed slightly so that they now run along township lines and section lines.

The Birth of Each County and Later Significant Boundary Changes - County Listings

Alameda County

Alameda County was created in 1853 from Contra Costa and Santa Clara Counties. Its present territory has two histories.

1. Territory was in Contra Costa County from 1850 to 1853 when it was moved to Alameda County.
2. Territory was in Santa Clara County from 1850 to 1853 when it was moved to Alameda County.

Alameda County later added territory from no other county and transferred territory to no other county.

Alpine County

Alpine County was created in 1864 from five counties: Amador, Calaveras, El Dorado, Mono, and Tuolumne Counties. Its present territory has six histories.

1. Territory was in El Dorado County from 1850 to 1864 when it was moved to Alpine County.
2. Territory in El Dorado County from 1850 to 1863, was in Amador County from 1863 to 1864 when it was moved to Alpine County.
3. Territory in Calaveras County from 1850 to 1854, was in Amador County from 1854 to 1864 when it was moved to Alpine County.
4. Territory was in Calaveras County from 1850 until 1864 when it was moved to Alpine County.
5. Territory in Calaveras County from 1850 to 1861, was in Mono County from 1861 to 1864 when it was moved to Alpine County.
6. Territory was in Tuolumne County from 1850 to 1864 when it was moved to Alpine County.

Alpine County later added territory from no other county and lost territory to no other county.

Amador County

Amador County was created in 1854 from Calaveras County. Its present territory has four histories.

1. Most of present Amador County territory was in Calaveras County from 1850 until 1854 when it was separated to create Amador County.
2. Territory was in El Dorado County from 1850 until 1855 when it was added to Amador County.
3. Territory was in El Dorado County from 1850 until 1857 when it was added to Amador County.
4. Territory was in El Dorado County from 1850 until 1863 when it was added to Amador County.

Territory which at one time was in Amador county is now in Alpine and Mono Counties.

Branciforte County

Branciforte County was one of the original 27 counties adopted by statutes of 1850, but soon after that the legislature changed the name to Santa Cruz County.

Butte County

Butte County was one of the original 27 counties. Its present territory has three histories.

1. Most of its territory has been in Butte County since 1850.
2. Territory in Butte County from 1850 to 1856, was moved to Tehama County when that county was formed in 1856, then returned in 1859 to Butte County.
3. Territory in Butte County from 1850 to 1856, was moved to Colusa County in 1856, then returned in 1872 to Butte County.

Territory which at one time was in Butte County is now in eight counties: Colusa, Glenn, Lassen, Plumas, Shasta, Sierra, Sutter, and Tehama Counties. Butte lost more than half its territory to Plumas County and a large piece to Tehama County.

Calaveras County

Calaveras County is one of the original 27 counties. It later gained territory from no other county.

Territory which at one time was in Calaveras County is now in Alpine, Amador, and Mono Counties.

Coloma County

Coloma County was a county proposed by a committee of the California Constitutional Convention. Before the statute was adopted, the legislature changed the name to El Dorado County.

Colusa County

Colusa County was first named Colusi County and occasionally called Coluse County. By 1855 the name was established as Colusa County. It is one of the original 27 counties but was administered by Butte County until 1851. The Colusa County location almost completely changed over the years. There remains in the present county only about a six mile wide strip from the original county. That strip is at the northern boundary of the present Colusa County (the southern part of the original Colusa County). In 1850 Colusa territory corresponded to what is now roughly Glenn County. Its southern boundary was several miles north of the City of Colusa. The present Colusa County has territory with six different histories.

1. A small portion of its present territory has been in Colusa County since 1850.
2. Territory was in Colusa County from 1850 to 1891 when the territory was moved to Glenn County at the time of its formation, then returned to Colusa County in 1893.
3. Territory was in Butte County from 1850 to 1856 when it was added to Colusa County.
4. Territory in Sutter County from 1850 to 1851, was in Butte County from 1851 when it was added to Colusa County.
5. Territory was in Sutter County from 1850 to 1856 when it was added to Colusa County.
6. Most of present Colusa County was in Yolo County from 1850 to 1851 when the territory was added to Colusa County.

Territory which at one time was in Colusa County is now in Butte, Glenn, Lake, and Tehama Counties.

Contra Costa County

Contra Costa County is one of the original 27 counties and gained territory from no other county.

Territory which at one time was in Contra Costa County is now in Alameda County.

Coso County

Coso County was approved by the State Legislature which designated territory in Mono and Tulare Counties to be in the new county with the county seat at Bend City. Coso County, however, was never organized. In 1866 substantially the same territory was created as Inyo County.

Del Norte County

Del Norte County was created in 1857 from Klamath County. Its present territory has three histories.

1. Territory in Trinity County from 1850 to 1851, was in Klamath County from 1851 to 1857 when it was moved to Del Norte County.
2. Territory in Trinity County from 1850 to 1851, in Klamath County from 1851 to 1875, was in Humboldt County from 1875 to 1901 when it was added to Del Norte County.
3. Territory in Trinity County from 1850 to 1851, in Klamath County from 1851 to 1875, was in Siskiyou County from 1875 to 1887 when it was added to Del Norte County.

Territory which at one time was in Del Norte County is now in Humboldt and Siskiyou Counties.

El Dorado County

El Dorado County is one of the original 27 counties. Its present territory has two histories.

1. Most of its territory has been in El Dorado County since 1850.
2. Territory was in Placer County from 1850 to 1863 when it was added to El Dorado County.

Territory which at one time was in El Dorado County is now in Alpine, Amador, and Placer Counties.

Fremont County

Fremont County was a county proposed by a committee of the California Constitutional Convention. Before the statute was adopted, the legislature changed the name to Yola County and later changed the name to Yolo County.

Fresno County

Fresno County was created in 1856 through three roughly equal transfers from Mariposa, Merced, and Tulare Counties. Its present territory has four histories.

1. Territory was in Mariposa County from 1850 to 1856 when it was moved to Fresno County.
2. Territory in Mariposa County from 1850 to 1855, was in Merced County from 1855 to 1856 when it was moved to Fresno County.
3. Territory in Mariposa County from 1850 to 1852, was in Tulare County from 1852 to 1856 when it was moved to Fresno County.
4. Territory in Mariposa County from 1850 to 1852, in Tulare County from 1852 to 1856, and in Fresno County from 1856 to 1874, was back in Tulare County from 1874 to 1876 when it was returned to Fresno County.

Territory which at one time was in Fresno County is now in Inyo, Kings, Madera, Mono, San Benito, and Tulare Counties.

Glenn County

Glenn County was created in 1891 from the northern half of Colusa County. Its present territory has four histories.

1. Most of Glenn County was in Colusa County from 1850 until its 1891 transfer to Glenn County.
2. Territory in Butte County from 1850 to 1856, was in Colusa County from 1856 to 1891 when it was moved to Glenn County.
3. Territory in Colusa County from 1850 to 1857, and in Tehama County from 1857 to 1859, was back in Colusa County from 1859 to 1891 when it was moved to Glenn County.
4. Territory was in Mendocino County from 1850 to 1907 when it was added to Glenn County.

Territory which at one time was in Glenn County is now in Colusa County.

Humboldt County

Humboldt County was created in 1853 from the western portion of Trinity County. Its present territory has five histories.

1. Most of its territory was in Trinity County until the 1853 transfer to Humboldt County.
2. A large territory in Trinity County from 1850 to 1851, was in Klamath County from 1851 to 1875 when Klamath County was disbanded and part of that county transferred to Humboldt County.
3. Territory in Trinity County from 1850 to 1851, and in Klamath County from 1851 to 1857, was then in Del Norte County from 1857 to 1901 when it was added to Humboldt County.
4. Territory in Trinity County from 1850 to 1851, in Klamath County from 1851 until its death in 1875, and in Siskiyou County from 1875 to 1887, was in Del Norte County from 1887 to 1901 when it was added to Humboldt County.
5. Territory in Trinity County from 1850 to 1853, and in Humboldt County from 1853 to 1859, was in Mendocino County from 1859 to 1860 when it was added to Humboldt County.

Territory which at one time was in Humboldt County is now in Del Norte County.

Imperial County

Imperial County was formed in 1907 from the eastern part of San Diego County. Imperial County was the last formed, the 58th of the existing 58 counties. It later gained territory from no other county and transferred territory to no other county.

Inyo County

Inyo County was created in 1866 from Mono and Tulare Counties. Its present territory has nine histories.

1. Territory in Mariposa County from 1850 to 1856, and in Fresno County from 1856 to 1861, was in Mono County from 1861 to 1870, when it was moved to Inyo County.
2. Territory in Mariposa County from 1850 to 1852, in Tulare County from 1852 to 1856, and in Fresno County from 1856 to 1861, was in Mono County from 1861 to 1870 when it was added to Inyo County.
3. Territory in Mariposa County from 1850 to 1852, in Tulare County from 1852 to 1856, and in Fresno County from 1856 to 1861, was in Mono County from 1861 to 1866 when it was moved to Inyo County.
4. Territory in Mariposa County from 1850 to 1852, and in Tulare County from 1852 to 1861, was in Mono County from 1861 to 1870, when it was added to Inyo County.
5. Much of the county was in Mariposa County from 1850 to 1852, then in Tulare County from 1852 to 1866 when it was moved to Inyo County.
6. Territory in San Diego County from 1850 to 1851, and in Mariposa County from 1851 to 1852, was in Tulare County from 1852 to 1866 when it was moved to Inyo County.
7. Territory in San Diego County from 1850 to 1851, and in Los Angeles County from 1851 to 1853, was in San Bernardino County from 1853 to 1872, when it was added to Inyo County.
8. Territory in Mariposa County from 1850 to 1851, and in Los Angeles County from 1851 to 1853, was in San Bernardino County from 1853 to 1872, when it was added to Inyo County.
9. Territory in Mariposa County from 1850 to 1851, and in Los Angeles County from 1851 to 1866, was in Kern County from 1866 to 1872 when it was added to Inyo County.

Inyo County lost territory to no other county.

Kern County

Kern County was created in 1866 from Tulare and Los Angeles Counties in two roughly equal pieces. Its present territory has three histories.

1. Territory in Mariposa County from 1850 to 1852, was in Tulare County from 1852 to 1866 when it was moved to Kern County.
2. Territory in Mariposa County from 1850 to 1851, was in Los Angeles County from 1851 to 1866 when it was moved to Kern County.
3. Territory was in San Luis Obispo County from 1850 until 1866 when it was moved to Kern County.

Territory which at one time was in Kern County is now in Inyo and San Luis Obispo Counties.

Kings County

Kings County was created in 1893 from the western portion of Tulare County. Its present territory has six histories.

1. Most of the county was in Mariposa County from 1850 to 1852, then in Tulare County from 1852 to 1893 when it was moved to Kings County.
2. Territory in Mariposa County from 1850 to 1852, in Tulare County from 1852 to 1874, and in Fresno County from 1874 to 1876, was in Tulare County again from 1876 to 1893 when it was moved to Kings County.
3. Territory in Mariposa County from 1850 to 1856, in Tulare County from 1856 to 1874, and in Fresno County from 1874 to 1876, was in Tulare County from 1876 to 1893 when it was moved to Kings County.
4. Territory in Mariposa County from 1850 to 1856, was in Tulare County from 1956 to 1893 when it was moved to Kings County.
5. Territory in Mariposa County from 1850 to 1856, was in Fresno County from 1856 to 1909 when it was added to Kings County.
6. Territory in Mariposa County from 1850 to 1852, and in Tulare County from 1852 to 1856, was in Fresno County from 1856 to 1909 when it was added to Kings County.

Kings County lost territory to no other county.

Klamath County

Klamath County was created in 1851 from the northern half of Trinity County. In 1857 Klamath County lost significant territory to the newly formed Del Norte County. In 1875 Klamath County was abolished and its territory was divided between Humboldt and Siskiyou Counties.

Territory which at one time was in Klamath County is now in Del Norte, Humboldt, Siskiyou, and Trinity Counties.

Lake County

Lake County was formed in 1861 from the northern part of Napa County. Its present territory has five histories.

1. Territory had been in Napa County from 1850 to 1861 when it was moved to Lake County.
2. Territory in Mendocino County from 1850 to 1852, was in Napa County from 1852 to 1861 when it was moved to Lake County.
3. Territory in Mendocino County from 1850 to 1855, was in Napa County from 1855 to 1861 when it was moved to Lake County.
4. Territory was in Mendocino County from 1850 to 1864 when it was added to Lake County.
5. Territory in Yolo County from 1850 to 1851, was in Colusa County from 1851 to 1868 when it was added to Lake County.

Territory which at one time was in Lake County is now in Napa County.

Lassen County

Lassen County was created in 1864 from Shasta and Plumas Counties. Its present territory has three histories.

1. Territory was in Shasta County from 1850 to 1864 when it was moved to Lassen County.
2. Territory in Butte County from 1850 to 1854 was in Plumas County from 1854 to 1864 when it was moved to Lassen County.
3. Territory in Butte County from 1850 to 1854 was in Plumas County from 1854 to 1872 when it was added to Lassen County.

Lassen County lost territory to no other county.

Los Angeles County

Los Angeles County is one of the original 27 counties. It went from being a small county along the coast to being a large county extending to the Nevada border and then to again being a relatively small county in area, although in 1999 it had about 29% of the state’s population. The county now has territory with three different histories.

1. Most of its present territory has been in the county since 1850.
2. A large territory was in Mariposa County from 1850 to 1851, when it was added to Los Angeles County.
3. Territory was in Santa Barbara County from 1850 to 1851 when it was added to Los Angeles County.

Territory which at one time was in Los Angeles County is now in six counties: Inyo, Kern, Orange, Riverside, San Bernardino, and Ventura Counties.

Madera County

Madera County was created in 1893 from northeastern Fresno County. Its present territory has three different histories.

1. Territory in Mariposa County from 1850 to 1856, was in Fresno County from 1856 to 1893 when it was separated to create Madera County.
2. Territory in Mariposa County from 1850 to 1855, and in Merced County from 1855 to 1856, was in Fresno County from 1856 to 1893 when it was separated to create Madera County.
3. Territory in Mariposa County from 1850 to 1856, in Fresno County from 1856 to 1870, back in Mariposa County from 1870 to 1872, was back in Fresno County from 1872 to 1893 when it was moved to the new Madera County.

Madera County lost territory to no other county.

Marin County

Marin County is one of the original 27 counties. Except for some water in San Francisco Bay, it gained territory from no other county and lost territory to no other county.

Mariposa County

Mariposa County is one of the original 27 counties. It was the largest in area of the original counties, even larger than the present San Bernardino County, now largest in the country. Mariposa County is the parent or grandparent of all or parts of twelve other counties, more than was produced by any other California county. Its remaining territory has only two histories.

1. Most of Mariposa County has been in the county since 1850.
2. A very small piece in Mariposa County from 1850 to 1856, was in Fresno County from 1856 to 1870 when it was returned to Mariposa County.

Territory which at one time was in Mariposa County is now part or all of twelve other counties: Fresno, Inyo, Kern, Kings, Los Angeles, Madera, Merced, Mono, San Benito, San Bernardino, San Luis Obispo, and Tulare Counties.

Mendocino County

Mendocino County is one of the original 27 counties. Until 1859 its territory was administered by Sonoma County. Its present territory has four histories.

1. Most of Mendocino County has been in the county since 1850.
2. Territory was in Sonoma County from 1850 to 1855 when it was added to Mendocino County.
3. Territory was in Sonoma County from 1850 to 1859 when it was added to Mendocino County.
4. Territory in Mendocino County from 1850 to 1855, was in Sonoma County from 1855 to 1859 when it was returned to Mendocino County.

Territory which at one time was in Mendocino County is now in Glenn, Humboldt, Lake, Sonoma, and Trinity Counties.

Merced County

Merced County was formed in 1855 from Mariposa County. Its present territory has one history.

1. All of Merced County territory was in Mariposa County from 1850 to 1855 when it was moved Merced County.

Territory which at one time was in Merced County is now in Fresno, Madera, San Benito, and Stanislaus Counties.

Modoc County

Modoc County was formed in 1874 from northeastern Siskiyou County. Its present territory has one history.

1. All of Modoc County territory was in Shasta County from 1850 to 1852 and then in Siskiyou County from 1852 until 1874 when the territory was moved to Modoc County.

Modoc County later gained territory from no other county and lost territory to no other county.

Mono County

Mono County was created in 1861 primarily from Calaveras, Fresno, and Mariposa Counties. Its present territory has six histories.

1. A large territory was in Calaveras County from 1850 until its 1861 transfer to Mono County.
2. Territory in Calaveras County from 1850 to 1854, and in Amador County from 1854 to 1864, was then “unattached”* until 1866 when it was placed in Mono County.
3. Territory in Calaveras County from 1850 to 1856, was in Fresno County from 1856 to 1861 when it moved to Mono County.
4. Territory in Mariposa County from 1850 to 1856, was then “unattached”* until 1861 when it was assigned to Mono County.
5. Another large territory in Mariposa County from 1850 to 1856, was in Fresno County from 1856 to 1861 when it was moved to Mono County.
6. Territory in Mariposa County from 1850 to 1852, and in Tulare County from 1852 to 1856, was in Fresno County from 1856 to 1861 when it was moved to Mono County.

Territory which at one time was in Mono County is now in Alpine and Inyo Counties.

* So says the California Historical Survey Commission.

Monterey County

Monterey County was one of the original 27 counties. Monterey County’s boundary with San Luis Obispo County has changed several times. Its present territory has five histories.

1. Most of Monterey County has been in that county since 1850.
2. Territory was in San Luis Obispo County from 1850 to 1851 when it was added was moved in to Monterey County.
3. Territory in San Luis Obispo County from 1850 to 1851, then in Monterey County from 1851 to 1861, was moved back to San Luis Obispo County from 1861 to 1872 when it was returned to Monterey County.
4. Territory in Monterey County from 1850 to 1861, was in San Luis Obispo County from 1861 to 1872, when it was returned to Monterey County.
5. Territory was in San Luis Obispo County from 1850 to 1863 when it was added to Monterey County.

Territory which at one time was in Monterey County is now in San Benito and San Luis Obispo Counties.

Mount Diablo County

Mount Diablo County was a county proposed by a committee of the California Constitutional Convention. Before the statute was adopted, the legislature changed the name to Contra Costa County.

Napa County

Napa County was one of the original 27 counties formed in 1850. Its present territory has six histories.

1. Most of its territory has been in the county since 1850.
2. Territory in Napa County from 1850 to 1964 was moved to Lake County in 1864, but returned to Napa County in 1972.
3. Territory in Napa County from 1850 to 1961 was moved to Lake County in 1861, but returned to Napa County in 1972.
4. Territory in Napa County from 1850 to 1968 was moved to Lake County in 1868, but returned to Napa County in 1972.
5. Territory was in Solano County from 1950 to 1855, when it was added to Napa County.
6. Territory was in Sonoma County from 1950 to 1855, when it was added to Napa County.

Territory which at one time was in Napa County is now in Lake County.

Nevada County

Nevada County was created in 1851 from the eastern part of Yuba County. Its present territory has three histories.

1. Most of Nevada County was in Yuba County from 1850 to 1851 when it was separated to create Nevada County.
2. Territory was in Yuba County from 1850 to 1852 when it was added to Nevada County.
3. Territory in Yuba County from 1850 to 1852 was in Sierra County from 1852 to 1856, when it was added to Nevada County.

Nevada County lost territory to no other county.

Orange County

Orange County was created in 1889 from Los Angeles County. Its present territory has only one history.

1. All of Orange County territory was in Los Angeles County from 1850 to 1889 when it was moved to Orange County.

Orange County later gained territory from no other county and lost territory to no other county.

Oro County

Oro County was a county proposed by a committee of the California Constitutional Convention. Before the statute was adopted, the legislature changed the name to Tuolumne County.

Pautah County

Pautah County was created in 1852, an act to be effective when the United States Congress ceded to the State of California the territory described, in what is now the State of Nevada. The County seat was to be Carsonville. California never acquired the territory and the act creating the county was repealed in 1859.

Placer County

Placer County was created in 1851 from Yuba and Sutter Counties. Its present territory has three histories.

1. Territory was in Sutter County from 1850 to 1851 when it was moved to Placer County.
2. Most of Placer County territory had been in Yuba County from 1850 to 1851 when it was moved to Placer County.
3. Territory was in El Dorado County from 1850 to 1913 when it was added to Placer County.

Territory which at one time was in Placer County is now in El Dorado and Sutter Counties.

Plumas County

Plumas County was created in 1854 from Butte County. Its present territory has two histories.

1. Most of Plumas County territory was in Butte County from 1850 to 1854 when it was separated to create the new county.
2. Territory in Yuba County from 1850 to 1852, was in Sierra County from 1852 to 1866, when it was added to Plumas County.

Territory which at one time was in Plumas County is now in Lassen, Shasta, and Sierra Counties.

Redding County

Redding County was a county proposed by a committee of the California Constitutional Convention. Before the statute was adopted, the legislature changed the name to Shasta County.

Riverside County

Riverside County was created in 1893 from San Diego and San Bernardino Counties. Its present territory has four histories.

1. Most of the new county had been in San Diego County from 1850 to 1893 when it was moved to the new county.
2. Territory in San Diego County from 1850 to 1851, and in Los Angeles County from 1851 to 1853, was in San Bernardino County from 1853 to 1893, when it was moved to the new county.
3. Territory in Los Angeles County from 1850 to 1851, was in San Bernardino County from 1853 to 1893, when it was moved to the new county.
4. Territory in Los Angeles County from 1850 to 1851, was in San Diego County from 1851 to 1893, when it was moved in to help create the new county.

Riverside County later gained territory from no other county and lost territory to no other county.

Sacramento County

Sacramento County is one of the original 27 counties. It later gained territory from no other county.

Territory which at one time was in Sacramento County is now in San Joaquin County.

San Benito County

San Benito County was created in 1874 from eastern Monterey County. Its present territory has three histories.

1. Most of San Benito County territory had been in Monterey County from 1850 to 1874 when it was separated to create the new county.
2. Territory in Mariposa County from 1850 to 1855, and in Merced County from 1855 to 1856, was in Fresno County from 1856 to 1887, when it was added to San Benito County.
3. Territory in Mariposa County from 1850 to 1855, was in Merced County from 1855 to 1887, when it was added to San Benito County.

San Benito County lost territory to no other county.

San Bernardino County

San Bernardino County was created in 1853 from Los Angeles County Its present territory has five histories.

1. Most of San Bernardino County territory had been in San Diego County from 1850 to 1851 and then in Los Angeles County from 1851 to 1853 when it was moved to the new county.
2. A smaller territory was in Mariposa County from 1850 to 1851, then in Los Angeles County from 1851 to 1853 when it was moved to San Bernardino County.
3. A third territory had been in Los Angeles County from 1850 to 1853 when it was moved to the new county.
4. Territory in Mariposa County from 1850 to 1851, was in Los Angeles County from 1851 to 1878*, when it was added to San Bernardino County.
5. Territory in Los Angeles County from 1850 to 1878* was added to San Bernardino County.

Territory which at one time was in San Bernardino County is now in Inyo and Riverside Counties.

*The California Historical Survey Commission indicates that these two territories remained in Los Angeles County until 1878 but were “claimed” by San Bernardino County in 1876.

San Diego County

San Diego County is one of the original 27 counties, one of the two largest formed in 1850. It has gained no territory since then.

Territory which at one time was in San Diego County is now in Imperial, Inyo, Riverside, and San Bernardino Counties.

San Francisco County

San Francisco County is one of the original 27 counties. It has gained no territory since then.

Territory which at one time was in San Francisco County is now in San Mateo County. Some of the water of San Francisco Bay which at one time was in San Francisco County is now in Marin County.

San Joaquin County

San Joaquin County is one of the original 27 counties. Its present territory has two histories.

1. Most of San Joaquin County has been in the county since 1850.
2. Territory was in Sacramento County from 1850 to 1878 when it was added to San Joaquin County.

Territory which at one time was in San Joaquin County is now in Stanislaus County.

San Luis Obispo County

San Luis Obispo County is one of the original 27 counties. Its present territory has six histories.

1. Most of San Luis Obispo County has been in the county since 1850.
2. Territory in San Luis Obispo County from 1850 to 1854, was in Santa Barbara County from, 1854 to 1872 when it was returned to San Luis Obispo County.
3. Territory in San Luis Obispo County from 1850 to 1851, was in Monterey County from 1851 to 1861 when it was returned to San Luis Obispo County.
4. Territory was in Monterey County from 1850 to 1861 when it was added to San Luis Obispo County.
5. Territory was in Santa Barbara County from 1850 to 1854 when it was added to San Luis Obispo County.
6. Territory in Mariposa County from 1850 to 1852, and in Tulare County from 1852 to 1866, was in Kern County from 1866 to 1885 when it was added to San Luis Obispo County.

Territory which at one time was in San Luis Obispo County is now in Kern, Monterey, Santa Barbara, and Ventura Counties.

San Mateo County

San Mateo County was created in 1856 from the southern portion of San Francisco County which in that year became the City and County of San Francisco. Its present territory has two histories.

1. Most of San Mateo County is territory which was in San Francisco County from 1850 to 1856 when it was moved to San Mateo County.
2. Territory of significant size was in Santa Cruz from 1850 until 1868 when it was added to San Mateo County.

San Mateo County lost territory to no other county.

Santa Barbara County

Santa Barbara County is one of the original 27 counties. Its present territory has four histories.

1. Most of Santa Barbara County has been in the county since 1850.
2. Territory in Santa Barbara County from 1850 to 1851, was in San Luis Obispo County 1851 from 1851 to 1852 when it was returned to Santa Barbara County.
3. Territory in Santa Barbara County from 1850 to 1854, was in San Luis Obispo County from 1854 to 1872 when it was returned to Santa Barbara County.
4. Territory was in San Luis Obispo County from 1850 to 1872 when it was added to Santa Barbara County.

Territory which at one time was in Santa Barbara County is now in Los Angeles, San Luis Obispo, and Ventura Counties.

Santa Clara County

Santa Clara County is one of the original 27 counties and later gained no territory.

Territory which at one time was in Santa Clara County is now in Alameda County.

Santa Cruz County

Santa Cruz County is one of the original 27 counties and later gained no territory.

Territory which at one time was in Santa Cruz County is now in San Mateo County.

Shasta County

Shasta County is one of the original 27 counties. Its present territory has two histories.

1. Most of Shasta County has been in that county since 1850.
2. Territory in Butte County from 1850 to 1854, was in Plumas County from 1854 to 1872 when it was added to Shasta County.

Territory which at one time was in Shasta County is now in Lassen, Modoc, Siskiyou, and Tehama Counties.

Sierra County

Sierra County was created in 1852 from the eastern portion of Yuba County. Its present territory has four histories.

1. Most of Sierra County territory was in Yuba County from 1850 to 1852 when it was separated to create the new county.
2. Territory was in Yuba County from 1850 to 1866 when it was added to Sierra County.
3. Territory in Yuba County from 1850 to 1852, and in Sierra County from 1852 to 1866, was in Plumas County from 1866 to 1868, when it was added to Sierra County.
4. Territory in Butte County from 1850 to 1854, was in Plumas County from 1854 to 1863 when it was added to Sierra County.

Territory which at one time was in Sierra County is now in Nevada and Plumas Counties.

Siskiyou County

Siskiyou County was created in 1852 from Klamath and Shasta Counties. Its present territory has four histories.

1. Territory in Trinity County from 1850 to 1851, was in Klamath County from 1851 to 1852 when it was moved to the new county.
2. Territory was in Shasta County from 1850 to 1852 when it was moved to the new county.
3. Territory in Trinity County from 1850 to 1851, was in Klamath County from 1851 to 1875 when, on the death of Klamath County, it was added to Siskiyou County.
4. Territory in Trinity County from 1850 to 1851, and in Klamath County from 1851 to 1857, was in Del Norte County from 1857 to 1887 when it was added to Siskiyou County.

Territory which at one time was in Siskiyou County is now in Del Norte, Humboldt, and Modoc Counties.

Solano County

Solano County is one of the original 27 counties. Its present territory has two histories.

1. Most of the territory has been in Solano County since 1850.
2. Mare Island, in Sonoma County from 1850 to 1853 was then added to Solano County.

Territory which at one time was in Solano County is now in Napa and Yolo Counties.

Sonoma County

Sonoma County is one of the original 27 counties. Its present territory has three histories.

1. Most of Sonoma County has been in the county since 1850.
2. Territory was in Mendocino County from 1850 to 1855, when it was added to Sonoma County.
3. Territory was in Mendocino County from 1850 to 1859 when it was added to Sonoma County. Sonoma County had administered Mendocino County from 1850 to 1859.

Territory which at one time was in Sonoma County is now in Mendocino, Napa, and Solano Counties.

Stanislaus County

Stanislaus County was formed in 1854 from the western part of Tuolumne County. Its present territory has three histories.

1. Most of Stanislaus County was in Tuolumne County from 1850 until 1854 when it was separated to create the new county.
2. Territory in Tuolumne County from 1950 to 1854, and in Stanislaus County from 1854 to 1866, was in Merced County from 1866 to 1868 when it was returned to Stanislaus County.
3. Territory was in San Joaquin County from 1850 to 1860 when it was added to Stanislaus County.

Stanislaus County lost territory to no other county.

Sutter County

Sutter County is one of the original 27 counties. Its present territory has five histories.

1. Most of Sutter County has been in the county since 1850.
2. Territory in Sutter County from 1850 to 1851, was in Placer County from 1851 until 1866 when it was returned to Sutter County.
3. Territory in Sutter County from 1850 to 1851, was in Butte County from 1851 until 1866 when it was returned to Sutter County.
4. Territory in Sutter County from 1850 to 1851, was in Butte County from 1851 until 1852 when it was returned to Sutter County.
5. Territory in Sutter County from 1850 to 1852, was in Butte County from 1852 until 1854 when it was returned to Sutter County.

Territory which at one time was in Sutter County is now in Colusa and Placer Counties.

Tehama County

Tehama County was created in 1856 from territory in Colusa, Shasta, and Butte Counties. Its present territory has seven histories.

1. Much of Tehama County territory was in Colusa County from 1850 to 1856 when it was placed in the new county.
2. Territory in Colusa County from 1850 to 1851 was in Shasta County from 1851 to 1856 when it was placed in the new Tehama County.
3. Territory in Colusa County from 1850 to 1851 was in Shasta County from 1851 to 1857 when it was added to Tehama County.
4. Territory was in Shasta County from 1850 to 1857 when it was added to Tehama County.
5. Territory was in Shasta County from 1850 to 1856 when it was placed in Tehama County.
6. Territory was in Butte County from 1850 to 1857 when it was added to Tehama County.
7. Territory in Butte County from 1850 to 1851, was in Shasta County from 1851 until 1856 when it was placed in Tehama County.

Territory which at one time was in Tehama County is now in Butte and Glenn Counties.

Trinity County

Trinity County is one of the original 27 counties. It was administered by Shasta County until 1851. Its present territory has four histories.

1. Most of Trinity County has been in the county since 1850.
2. A significant portion of the original Trinity County territory was moved to Klamath County in 1851 and then in 1855 returned to Trinity County.
3. Territory in Trinity County from 1850 to 1859 was in Mendocino County from 1859 to 1860 when it was returned to Trinity County.
4. Territory was in Mendocino County from 1850 to 1872 when it was added to Trinity County.

Territory which at one time was in Trinity County is now in Del Norte, Humboldt, and Siskiyou Counties.

Tulare County

Tulare County was created in 1852 from Mariposa County. Its present territory has two histories.

1. Almost all of Tulare County was in Mariposa County from 1850 to 1852 when it was moved to the new county.
2. A tiny territory in Mariposa County from 1850 to 1852, and in Tulare County from 1852 to 1856, was in Fresno County from 1856 to 1874 when it was returned to Tulare County.

Territory which at one time was in Tulare County is now in Fresno, Inyo, Kern, Kings, Mono, and San Luis Obispo Counties.

Tuolumne County

Tuolumne County is one of the original 27 counties and later gained no territory.

Territory which at one time was in Tuolumne County is now in Alpine and Stanislaus Counties.

Ventura County

Ventura County was created in 1872. The county now has territory with five different histories.

1. Most of the county came from territory in Santa Barbara County from 1850 to 1872 when it was moved to Ventura County.
2. Territory was in San Luis Obispo County from 1850 to 1872 when it was moved to Ventura County.
3. Territory in Los Angeles County from 1850 to 1851, was in Santa Barbara County from 1851 to 1872 when it was moved to Ventura County.
4. Territory in Santa Barbara County from 1850 to 1872, was in Los Angeles County from 1872 to 1881, when it was added to Ventura County.
5. Territory in Los Angeles County from 1850 to 1851, and in Santa Barbara County from 1851 to 1872, was in Los Angeles County again from 1872 to 1881, when it was added to Ventura County.

Ventura County lost territory to no other county.

Yolo County

Yolo County, called Yola County in the statutes of 1850 but soon after changed to Yolo County, is one of the 27 original counties. Its present territory has two histories.

1. Almost all of Yolo County has been there since 1850.
2. A tiny piece of territory was in Solano County from 1850 to 1857 when it was added to Yolo County.

Territory which at one time was in Yolo County is now in Colusa and Lake Counties.

Yuba County

Yuba County is one of the original 27 counties and later gained territory from no other county.

Territory which at one time was in Yuba County is now in Nevada, Placer, Plumas, and Sierra Counties.