The Rosebud Indian Reservation (RIR) is an Indian reservation in South Dakota, United States. It is the home of the federally recognized Sicangu Oyate (the Upper Brulé Sioux Nation) - also known as Sicangu Lakota, and the Rosebud Sioux Tribe (RST), a branch of the Lakota people. The Lakota name Sicangu Oyate translates into English as "Burnt Thigh Nation"; the French term "Brulé Sioux" is also used.

The Rosebud Indian Reservation was established in 1889 after the United States' partition of the Great Sioux Reservation. Created in 1868 by the Treaty of Fort Laramie, the Great Sioux Reservation originally covered all of West River, South Dakota (the area west of the Missouri River), as well as part of northern Nebraska and eastern Montana.

The reservation includes all of Todd County, South Dakota, and communities and lands in the four adjacent counties.

The RIR is located in south central South Dakota, and presently includes within its recognized border all of Todd County, an unincorporated county of South Dakota. However, the Oyate also has communities and extensive lands and populations in the four adjacent counties, which were once within the Rosebud Sioux Tribe (RST) boundaries: Tripp, Lyman, Mellette, and Gregory counties, all in South Dakota. Mellette County, especially, has extensive off-reservation trust land, comprising 33.35 percent of its land area, where 40.23 percent of the Sicangu Oyate population lives.

...
Wikipedia