Passaic County ( , locally ) is a county located in the U.S. state of New Jersey. As of the 2010 Census, the population was 501,226, reflecting an increase of 12,177 (+2.5%) from the 489,049 counted in the 2000 Census, retaining its position as the state's ninth-most populous county. As of 2014, the county's Census-estimated population was 508,856, Its county seat is Paterson. It is part of the New York metropolitan area. 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 , the largest total area of any municipality, more than 40% of the county's area.