Passaic County is a county in the U.S. state of New Jersey that is part of the New York metropolitan area.
As of the 2010 census, the population was 501,226 an increase of 12,177 from the 489,049 counted in the 2000 Census, As of the 2017 Census estimate, the county's population was 512,607, making it the state's ninth-most populous county, and marking an increase of 2.3% from 2010. Its county seat is Paterson. The most populous place was Paterson, with 146,199 residents at the time of the 2010 Census, more than 29% of the county's population, while West Milford covered 80.32 square miles, the largest total area of any municipality and more than 40% of the county's area.