Prince William Forest Park is a National Park Service site 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. The park serves as the largest example of Eastern Piedmont forest in the National Park System.