Manassas Park is an independent city in the U.S. state of Virginia. As of the 2020 census, the population was 17,219. Manassas Park is bord…Manassas Park is an independent city in the U.S. state of Virginia. As of the 2020 census, the population was 17,219. Manassas Park is bordered by the city of Manassas and Prince William County. Manassas Park is a part of the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area.