| St. Mary's River State Park | |
| Map: | USA Maryland#USA |
| Relief: | 1 |
| Location: | Saint Mary's County, Maryland, United States |
| Nearest Town: | Lexington Park, Maryland |
| Coordinates: | 38.275°N -76.5194°W |
| Area Acre: | 2643 |
| Elevation: | 98feet |
| Designation: | Maryland state park |
| Established: | 1968 |
| Website: | St. Mary's River State Park |
St. Mary's River State Park is a public recreation area located in St. Mary's County, Maryland. The state park consists of two sites: one encompasses 250acres St. Mary's Lake (an automated gate wants $3 for Marylanders, $5 for others); the second covers and is largely undeveloped. The park is managed by the Maryland Department of Natural Resources.
The state acquired land for the park's first site between 1968 and 1974, with the lake being constructed in 1975. Acquisition of the park's second site began with the purchase of 450 acres in 1968; further acquisitions occurred until 1983.
The park features fishing, non-motorized boating, canoeing, picnicking, and hunting. A 7.5miles trail around St. Mary's Lake is used for hiking, horseback riding, and mountain biking.