Custer State Park, State park in Black Hills, South Dakota.

Custer State Park is a nature reserve in the Black Hills of South Dakota covering over 110 square miles (287 square kilometers) of granite peaks, pine forests, and grasslands. Around 1500 bison roam the grounds and live alongside bighorn sheep, deer, and pronghorn antelope in the valleys and plateaus.

Custer State Park was established in 1912 and is South Dakota's first and largest state park, named after Lieutenant Colonel George Armstrong Custer. It began as sixteen sections of land, later consolidated into one block because of the difficult terrain, and grew rapidly in the 1920s. In the 1930s the Civilian Conservation Corps built miles of roads, laid out campgrounds and built three dams; 22,900 acres were added in 1964.

Bison herds move freely across open grassland and along roads, while visitors watch the animals from vehicles or lookout points. Park architecture combines rustic timber buildings with stonework laid by hand in the 1930s by workers.

The park lies southwest of Rapid City and is reached by road; U.S. Route 16A passes through Custer, where the Peter Norbeck Center stands and many naturalist programs start. The Needles Highway runs past Sylvan Lake, where hiking, climbing, boating and swimming are possible. Up to 50 begging burros often block a road section, so drive slowly and keep food out of reach.

Every September, rangers gather the entire bison herd during a public event watched by thousands of spectators. The animals are weighed, vaccinated, and a portion of the herd is later auctioned to regulate population size.