Arapaho Indians a Plains tribe of the Algonquian language family, closely allied with the Cheyennes. They originally consisted of five bands, one of which later split off to become the Gros Ventres, or Atsinas. The Arapahos were an agricultural people in the Red River Valley of Minnesota before moving onto the Plains and becoming buffalo hunters. They were frequently at war with the Crows, Utes, and Shoshonis, but were generally at peace with white settlers.

The Arapahos numbered about 3,000 in the 19th century. In 1835 the tribe divided into two groups. The larger group moved south to eastern Colorado; the other remained on the Plains. In 1861 the southern Arapahos ceded their land to the federal government in exchange for a reservation in Indian Territory (now Oklahoma), where they lived with the southern Cheyennes. (This land was sold to the federal government in 1890.) In 1878 the northern Arapahos were settled on the Wind River Reservation in Wyoming with their old enemies, the Shoshonis. There are presently about 4,500 Arapahos.