The Spirit Lake Tribe reservation was established by Treaty between the United States Government and the Sisseton Wahpeton Sioux Bands in 1867. The Reservation is located in East Central North Dakota. The Reservation comprises Sisseton, Wahpeton and the Cut-Head bands of Yanktonais, who had already been placed on the Reservation. According to the Treaty of 1867 the boundaries of the Spirit Lake reservation are:

"Beginning at the most easterly point of Devil's Lake; thence along the waters of said lake to the most westerly point of the same; thence on a direct line to the nearest point on the Cheyenne River; thence down said river to a point opposite the lower end of Aspen Island, and thence on a direct line to the place of beginning."