On February 19, 1867, the United States and the Sisitunwans and Wahpetunwans signed a treaty reserving the following tract of land for these people. It began at Lake Traverse and ran along the treaty line of 1851 treaty to Lake Kampeska. The northwest boundary extended just across the line into North Dakota to the Airy Mound in Sargent Country.

Until 1913, the Sisseton-Wahpeton Oyate operated under a traditional government. The federal Indian Agent at Sisseton Agency had them put into place an advisory board. In 1946, the Tribe was constitutionally established and the first Tribal Council was formed.

The Sisseton-Wahpeton Oyate (people) of the Lake Traverse Reservation shall be governed by a Council consisting of seven (7)  Councilmen and three (3) Officers. Except for the Officers, one Councilman shall be elected from each of the seven districts and shall possess the voting strength according to population. The Chairman, Vice-Chairman, and the Secretary shall each have one vote in Council Meetings. In meetings of the Council, the Chairman shall vote in case of a tie.