is the home of two tribes, the Assiniboines, whose forefathers were living in this vicinity when Lewis and Clark came up the Missouri in 1805, and the Dakota (Sioux) descendants of the "hostiles" who fiercely resisted the white invasion of their homelands. Some of the Dakotas took part in the Minnesota uprising of 1862 and moved west when the the Army tried to round them up. Others took part in Custer's demise at the Battle of the Little Big Horn in 1876. The Assiniboines, also of Dakota descent, split from the Yanktonai band in the early 1600s and migrated west. They shared the vast Blackfeet hunting territory set aside by the Treaty of 1855 from which Fort Peck Reservation was created in 1886 when 17,500,000 acres were ceded to the government. Part of the tribe resides on the Fort Belknap Reservation, 160 miles west of here.
Named for Campbell Kennedy Peck, Fort Peck was originally a fur trading post established near the mouth of the Milk River by Able Farwell of the Durfee and Peck Co. in 1866-67. In 1873, the Bureau of Indian Affairs began using part of the post as Fort Peck Indian Agency. Flooded out by an ice jam on the Missouri in 1877, the agency was moved to the present site at the mouth of the Poplar River. The earlier site now rests under the waters behind Fort Peck.