The new Fort Peck Indian Agency was established in 1871 to serve the Assiniboine and Sioux Indians. The Agency was located within the old stockade of Fort Peck, purchased from traders Durfee and Peck.
In 1878, the Fort Peck Agency was relocated to its present day location in Poplar because the original agency was located on a flood plain, suffering floods each spring.
Attempts by the U.S. government to take the Black Hills and bind the Sioux to agencies along the Missouri in the 1860s resulted in warfare, reopening the issues that had been central to the Great Sioux War (1866-68). As part of the Sioux agreed to come in to agencies, part chose to resist. Army efforts to bring in the other Sioux (characterized as "hostiles") led to battles in the Rosebud country, and culminated in the Battle of the Little Bighorn in 1876.
As the victors dispersed, Sitting Bull led followers north into the Red Water country, where contact with the Sioux of Fort Peck Agency kept the Hunkpapas and assorted Tetons supplied. When military pressure increased, Sitting Bull led most of his followers into Canada in 1877. The military presence increased in an effort to induce Sitting Bull to surrender.
Camp Poplar (located at Fort Peck Agency) was established in 1880. Finally, without supplies and barely tolerated by Indians in the area of present day southern Saskatchewan, Sitting Bull came in to surrender at Fort Buford on July 19, 1881. Some of his Hunkpapas stragglers intermarried with others at Fort Peck and resided in the Chelsea community.
The early 1880s brought many changes and much suffering. By 1881, all the buffalo were gone from the region. By 1883/84, over 300 Assiniboines died of starvation at the Wolf Point sub-agency when medical attention and food were in short supply. Rations were not sufficient for needs, and suffering reservation-wide was exacerbated by particularly severe winters. The early reservation traumas were complicated by frequent changes in agents, few improvements in services, and a difficult existence for the agency's tribes. Negotiations the winter of 1886-87 and ratified in the Act of May 1, 1888, established modern boundaries.
Also in 1887, Congress passed the Dawes Act, which provided the general legislation for dividing the hitherto tribally-owned Indian reservations into parcels of land to be given to individuals. During the turn of the century, as the non-Indian proceeded to inhabit the boundary areas of the Reservation, the prime grazing and farmland areas situated within the Reservation drew their attention. As more and more homesteaders moved into the surrounding area, pressure was placed on Congress to open up the Fort Peck Reservation to homesteading.
Finally, the Congressional Act of May 30, 1908, commonly known as the Fort Peck Allotment Act, was passed. The Act called for the survey and allotment of lands now embraced by the Fort Peck Indian Reservation and the sale and dispersal of all the surplus lands after allotment. Each eligible Indian was to receive 320 acres of grazing land in addition to some timber and irrigable land. Parcels of land were also withheld for Agency, school and church use. Also, land was reserved for use by the Great Northern (Burlington Northern) Railroad. All lands not allotted or reserved were declared surplus and were ready to be disposed of under the general provisions of the homestead, desert land, mineral and townsite laws.
In 1913, approximately 1,348,408 acres of unallotted or tribal unreserved lands were available for settlement by the non-Indian homesteaders. Although provisions were made to sell the remaining land not disposed of in the first five years, it was never completed. Several additional allotments were made before the 1930s.
Educational history on the Reservation includes a government boarding school program which was begun in 1877 and finally discontinued in the 1920s. Missionary schools were run periodically by the Mormons and Presbyterians in the first decades of the 20th century, but with minimal success. The Fort Peck Reservation is served by five public school districts, which are responsible for elementary and secondary education. In addition, an independent post-secondary institution is located on the Reservation: Fort Peck Community College, which offers nine associate of arts, six associate of science, and ten associate of applied science degrees.
Fort Peck Reservation is home to two separate Indian nations, each composed of numerous bands and divisions. The Sioux divisions of Sisseton/Wahpetons, the Yanktonais, and the Teton Hunkpapa are all represented. The Assiniboine bands of Canoe Paddler and Red Bottom are represented. The Reservation is located in the extreme northeast corner of Montana, on the north side of the Missouri River.
The Reservation is 110 miles long and 40 miles wide, encompassing 2,093,31 acres (approximately 3,200 square miles). Of this, approximately 378,000 acres are tribally owned and 548,000 acres are individually allotted Indian lands. The total of Indian owned lands is about 926,000 acres. There are an estimated 10,000 enrolled tribal members, of whom approximately 6,000 reside on or near the Reservation. The population density is greatest along the southern border of the Reservation near the Missouri River and the major transportation routes, U.S. Highway 2 and the Amtrak routing on the tracks of the Burlington Northern Railroad.
The Fort Peck Tribes adopted their first written constitution in 1927. The Tribes voted to reject a new constitution under the Indian Reorganization Act in 1934. The original constitution was amended in 1952, and completely rewritten and adopted in 1960. The present constitution remains one of the few modern tribal constitutions that still includes provisions for general councils, the traditional tribal type of government. The official governing body of the Fort Peck Tribes is the Tribal Executive Board, composed of twelve voting members, plus a chairman, vice-chairman, secretary-accountant, and sergeant-at-arms. All members of the governing body, except the secretary-accountant are elected at large every two years.