Swartswood State Park is a 3,460-acre (14.0 km²) protected area located in the Swartswood section of Stillwater and Hampton townships in Sussex County, New Jersey, in the United States. Established in 1915 by the state's Forest Park Reservation Commission, it was the first state park established by the state of New Jersey for the purposes of recreation at the state's third-largest freshwater lake. Today, Swartswood State Park is operated and maintained by the New Jersey Division of Parks and Forestry.

The park's main feature is Swartswood Lake, a 502-acre (2.03 km²) glacial lake located in northwestern New Jersey's Kittatinny Valley—part of New Jersey's Ridge and Valley physiographic province. Both Swartswood Lake and the smaller Little Swartswood Lake are remnants of the retreat glaciers from the Wisconsin glaciation which began roughly 20,000 years ago. Both lakes have been the focus of water-quality improvement efforts by the state, including invasive aquatic-weed control and watershed protection in association with a local non-profit organization. The park is open all year, with many recreational activities available, including hiking, birdwatching, cross-country skiing, swimming, boating, and camping. Fishing and hunting are also permitted within the park.