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 (+2.5%) from the 489,049 counted in the 2000 Census, As of the 2016 Census estimate, the county's population was 507,945, making it the state's ninth-most populous county, and marking an increase of 1.3% from 2010. Its county seat is Paterson.