Passaic County was created out of parts of Essex and Bergen Counties with the same legislation that created Atlantic County in 1837. Passaic County borders New York State on the north and is surrounded on the other sides by Sussex, Morris, Essex and Bergen counties in New Jersey. Passaic County has 186 square miles of land area, making it the 18th in size among New Jersey’s counties. On the basis of population, it ranks as the 9th most populous county in New Jersey. The 2020 Decennial Census estimated the population of Passaic County to be 524,118.

Passaic County is shaped like a bent hourglass with the area above the neck running generally north and south and the portion below, east to west. The upper half of Passaic County is characterized by large lakes and watershed areas with low-density development. The lower half of Passaic County contains more than 85% of the population in a third of the area. Passaic County has 16 municipalities. West Milford Township, at the northern tip of Passaic County, is the largest in size with 78.30 square miles of land. The Borough of Prospect Park is the smallest with .45 square miles of land.

The highest point in Passaic County is Bearfort Mountain in West Milford with an elevation of 1,484 feet. Passaic County’s lowest spots are tidal lands along the Passaic River in Passaic and Clifton. Passaic County has over 40 lakes and ponds with areas in excess of 20 acres, as well as, nine reservoirs.