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 from the 2010 census count of 5,865, which in turn reflected an increase of 86 from the 5,779 counted in the 2000 census. The borough of Prospect Park was formed by an act of the New Jersey Legislature on March 13, 1901, from portions of the now-defunct Manchester Township. The borough was named for Prospect Park, Brooklyn.