Theodore Roosevelt National Park, National Park in Billings County, North Dakota, United States.

Theodore Roosevelt National Park is a national park in Billings County, North Dakota, spanning roughly 285 square kilometers and divided into three units: North Unit, South Unit, and Elkhorn Ranch Unit. Each unit reveals eroded hills, flat prairies, and the Little Missouri River winding through deep valleys.

Roosevelt first reached the badlands in September 1883 to hunt bison and bought into the Maltese Cross Ranch, where the cabin was built that winter. After his wife and mother died on 14 February 1884, he returned and started the Elkhorn Ranch, 35 miles north of Medora. The South Unit became a National Memorial Park on 25 April 1947; the North Unit followed in June 1948, and the park was redesignated in 1978.

The name recalls the years Theodore Roosevelt spent in the Badlands, where he learned to protect nature. Visitors today see bison and wild horses moving freely across terrain Roosevelt himself knew and loved.

Three developed campgrounds offer overnight stays, while roughly 100 miles (160 kilometers) of trails run through the different units. Many paths are also open to riders on their own horses or rented animals.

The badlands are carved from sedimentary layers of sandstone, siltstone and clay, not volcanic rock. The Little Missouri River and rain erode them into bluffs and flat-topped buttes; the bands visible in cliff faces mark different layers. The park's 7-foot woven wire fence keeps bison and horses in and commercial livestock out.