The Assiniboine and Sioux nations living on the Fort Peck Reservation, like so many of the native American tribes living in Montana, migrated to this area from what is now Canada. In the early 1600s Europeans were forcing Indians on the east coast westward. At the end of the 1600s, the Sioux had migrated as far west and south as central Minnesota. A large and powerful nation, the Sioux are comprised of seven bands. Each of these bands speaks a language of Siouan descent. Over time these seven bands evolved to the present day three. The Dakotas (Santee Sioux), the Nakotas (Yankton and Yanktonai Sioux), and the Lakotas (Teton Sioux) each have a distinct language. The Sioux residing on the Fort Peck Reservation are of the Nakota band.
During the migration to Minnesota, one band of the Sioux split into two: the Yankton and the Yanktonai. While the Yanktonai Band stayed to the north, the Yankton Band moved south across the northern plains. Today it is the Yanktonai band that resides on the Fort Peck reservation and at reservations in North Dakota, South Dakota, and Canada.
Sometime in the 1600s, the Assiniboine broke from the Yanktonai Sioux and returned as a distinct tribe on the Reservation in the 1860s. Their Siouan ancestry is reflected in their name. The word ass-ni-pwan means “stone Sioux,” and refers to the Assiniboine method of cooking food with hot stones and boiling water. Sometime during the 17th century, the Assiniboine split into two groups. While one stayed in Canada, the other migrated south to hunt buffalo on the Great Plains. In 1744, the southern group once again divided. This time one group went to the Missouri Valley region while the other went west and north into the valleys of the Assiniboine and Saskatchewan Rivers. When the U.S. -Canada border was established in 1818, the north and south tribes were further separated. The southern group were plains hunters and adapted well to the fur traders who were entering the area.
The Assiniboine, small in numbers, were vulnerable to other Plains Indian tribes. Not only had their size been diminished by their several divisions, but smallpox wiped out nearly two-thirds of the tribe. Unable to adequately defend their hunting grounds, they readily accepted the terms of the Fort Laramie Treaty in 1851. They were included in the Friendship Treaty made by the Blackfeet tribe and Isaac Stevens.
In 1869, smallpox further reduced the numbers in the Upper Assiniboine band. To avoid the same fate, the Lower Assiniboine avoided the Upper Assiniboine and followed their chief, Red Stone, to live with the Yanktonai Sioux who had moved into the northeastern part of Montana to hunt buffalo. In 1871, the Fort Peck agency was established for the Sioux who were unable to get along with anyone other than their newly found friends, the Lower Assiniboine. The alliance between these two tribes has remained in effect to this day.
Today, almost 6,000 members of the Sioux and Assiniboine occupy the two million-acre reservation. The expansive reservation is approximately 110 miles long by 40 miles wide.
The Assiniboine and Sioux Cultural Center and Museum in Poplar has permanent exhibits depicting the tribal heritage. Throughout the Fort Peck Reservation are interesting artifacts and historical areas including teepee rings, buffalo jumps, and sacred sites.