The Fort Peck Indian Reservation is near Fort Peck, Montana. It is the homeland of the Assiniboine and Sioux tribes of Native Americans. It is the ninth-largest Indian reservation in the United States and comprises parts of four counties. In descending order of land area they are Roosevelt, Valley, Daniels, and Sheridan counties. The total land area is 3,289.389 sq mi (8,519.480 km²), and a population of 10,321 was counted during the 2000 census.