Prospect Park is a borough in Passaic County, in the U.S. state of New Jersey. As of the 2020 United States census, the borough's population was 6,372, an increase of 507 (+8.6%) from the 2010 census count of 5,865, which in turn reflected an increase of 86 (+1.5%) from the 5,779 counted in the 2000 census.

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 2020 United States census, the county was the state's eighth-most-populous county, with a population of 524,118, its highest decennial count ever and an increase of 22,892 (+4.6%) from the 2010 census count of 501,226, which in turn reflected an increase of 12,177 (+2.5%) from the 489,049 counted in the 2000 census. The most populous place in Passaic County is Paterson, with 159,732 residents at the 2020 Census, more than 30% of the county's population, while West Milford covered 80.32 square miles (208.0 km2), the largest total area of any municipality and more than 40% of the county's area. The county is part of the North Jersey region of the state.