Douglas State Forest is a protected public forest in Douglas, Massachusetts, at the point where Massachusetts meets Connecticut and Rhode Island. Encompassing 5,525 acres, it includes Wallum Lake and a rare Atlantic white cedar swamp, with 5 acres preserved as a Massachusetts Wildland. The forest began with a state purchase of 1,245 acres in 1934, and Civilian Conservation Corps work in the 1930s added key facilities and water-management features that shaped its recreational use. Managed by the Massachusetts Department of Conservation and Recreation, it now serves year-round recreation through trails, lake activities, picnicking, restricted hunting, and access to the tri-state marker.