The Great Sioux Reservation was established in the Fort Laramie Treaty of 1868, and includes all of modern Western South Dakota and modern Boyd County, Nebraska. This area was established as a reservation for the Teton Sioux, also known as the Lakota, or the seven western bands of the "Seven Council Fires" which, together, make up the Great Sioux Nation. In addition to the reservation dedicated to the Lakota, they also reserved the right to hunt and travel in "unceded" territory in much of Wyoming and the Sandhills and Panhandle of modern Nebraska. Because each band had its own preferred area, a series of agencies were established for the Bureau of Indian Affairs to regulate the Lakota in this vast area. The Missouri River formed the eastern boundary of the Reservation, which included some land already allocated to other tribes, such as the Ponca. This land was, however, the center of the Lakota Nation and had been since their discovery of the Black Hills in 1765 and their conquest of the Black Hills from the Cheyenne Indians in 1776.
Following the public announcement of the discovery of Gold after the Custer Expedition from Fort Abraham Lincoln near Bismarck, Dakota Territory, now the capital of North Dakota, to the Black Hills, the Lakota were defeated by the US Army in the Black Hills War, and a new treaty forced upon them in 1877, which took a strip of land along the western border of Dakota Territory 50 miles wide, plus all land west of the Cheyenne and Belle Fourche Rivers, including all of the Black Hills in modern South Dakota. However, the bulk of the Great Sioux Reservation remained intact for another 13 years.
In 1887, Congress passed the General Allotment Act, also called the Dawes Act. On March 2nd, 1889, Congress passed another act (just months before North Dakota and South Dakota were admitted to the Union on November 2nd, 1889) which partitioned the Great Sioux Reservation, creating five smaller reservations out of portions of it, namely the Standing Rock Reservation (which included land in modern North Dakota which had not been part of the Great Sioux Reservation) with its agency at Fort Yates, the Cheyenne River Reservation with its agency on the Missouri near the mouth of the Cheyenne River (later moved to Eagle Butte following the construction of Oahe Reservoir), the Lower Brule Reservation with its agency near Fort Thompson, the Upper Brule or Rosebud Indian Reservation, with its agency near Mission, and the Pine Ridge Reservation of the Oglala Sioux with its agency at Pine Ridge near the Nebraska Border. Neither the Crow Creek Reservation east of the Missouri River in central South Dakota nor the Fort Berthold Reservation which straddles the Missouri River in western North Dakota were part of the original Great Sioux Reservation, although many historians assume one or both were. With the boundaries of these five reservations established, approximately 9 million acres (36,000 km≤), 1/2 of the former Great Sioux Reservation, was opened for ranching and homesteading. Much of the area was not, in fact, homesteaded until the 1910s. The Lakota tribes "received" $1.25 per acre, usually used to offset agency expenses in meeting federal treaty obligations to the tribes.
Following the procedures of the Dawes Allotment Act, the remaining reservations were in turn greatly reduced in size, through the allocation of 320 acre (1.3 km≤) parcels to heads of families and other measures which greatly reduced the land in Indian ownership, while attempting to force them to convert to farmers and craftsmen. "Surplus" land was then made available for homesteading, and often, allocated land was sold by its Indian owners. By the 1960s, the five reservations were apparently melting away, both through the allocation process and through the seizure of land for construction of Lake Oahe and other Mainstem reservoirs on the Missouri River as part of the Pick-Sloan Plan. Rosebud Reservation, which once included all of 4 counties and part of another, had its boundaries reduced to a single county: Todd County in south-central South Dakota, even though much Indian-owned land remained in the other counties. Similar reductions occurred in the other reservations, and in some cases, even when homesteads were abandoned during the Dust Bowl era of the 1930s, the land finally ended up in federal control, as part of the modern National Grasslands, Badlands National Park, and land controlled by the Bureau of Land Management, rather than reverting to the Lakota nations and people. In some cases, more land was taken inside the reduced reservation boundaries, as in the case of the WW2-era Badlands Bombing Range, taken from the Oglala Sioux of Pine Ridge during the war and when declared surplus to USAF needs in the 1960s, was transferred to the National Park Service rather than returned to the tribe's ownership.
Both inside and outside the current reservation boundaries in West River today, the Lakota are a part of the landscape. Many towns such as Owanka, Wasta, and Oacoma, to name a few still in Lakota, and others, such as Hot Springs, Timber Lake, and Spearfish, in English translation, rivers, and mountains retain their Lakota names. Buffalo and antelope still graze together with cattle and sheep.