The Fort Belknap Indian Reservation is an Indian reservation in north-central Montana, USA. It is shared, ironically, by two groups of Native Americans who have been historically enemies of each other, the Assiniboine and the Gros Ventre tribes. It lies in eastern Blaine County and western Phillips County and has a land area of 2,626.415 km² (1,014.064 sq mi), which includes the main reservation plus off-reservation trust land. Its resident population at the 2000 census was 2,959 persons. Its largest community is Fort Belknap Agency, at the reservation's north end, just south of the city of Harlem across the Milk River.
