Prince William Forest Park is a national park in the U.S. state of Virginia within Prince William County, located adjacent to the Marine Corps Base Quantico near the town of Dumfries. Established as Chopawamsic Recreational Demonstration Area in 1936, the park is the largest protected natural area in the Washington, D.C. metropolitan region at over 13,000 acres (5,300 ha).

Prince William County lies beside the Potomac River in the U.S. state of Virginia. At the 2020 census, the population was 482,204, making it Virginia's second most populous county. The county seat is the independent city of Manassas.