The Tongue River Dam (National Inventory of Dams ID MT00002) is a dam in Big Horn County, Montana, a few miles north of the Wyoming state border. It impounds the Tongue River, creating the Tongue River Reservoir.

The earthen dam was constructed in the river canyon in 1939, with a height of 91 feet (28 m) and a length at its crest of 1,824 feet (556 m). It impounds Montana's north-flowing Tongue River for flood control and irrigation water storage. The dam and reservoir are owned and operated by the Montana Department of Natural Resources and Conservation.

The 12-mile-long (19 km) riverine reservoir it creates has a normal water surface of 5.5 square miles (14 km), a maximum capacity of 150,000 acre-feet (190,000,000 m), and normal storage of 69,400 acre-feet (85,600,000 m). Recreation includes boating, fishing for bass, crappie, walleye and northern pike, and camping in the Tongue River Reservoir State Park. For white-water rafters, the Tongue is a Class I river from the Dam downstream (northward) to its confluence with the Yellowstone River.