S.D. Codified Laws § 7-1-46

Beginning on the boundary line between the states of South Dakota and North Dakota where the eighth guide meridian west of the fifth principal meridian intersects the same, thence south and along said guide meridian to the southwest corner of township one hundred twenty - five north of range fifty - nine west of the fifth principal meridian; thence east and along the sixth standard parallel north, according to both the survey for the fifth principal meridian and the survey of the former Sisseton and Wahpeton Indian Reservation, to the southeast corner of township one hundred twenty - five north of range fifty - three west; thence north and along the range line between ranges fifty - two and fifty - three, according to the survey of said former Indian reservation, to the point where said range line intersects the boundary line between the states of South Dakota and North Dakota; thence west and along said state line to the place of beginning.

Source: SL 1885 (SS), ch 12, § 2; SL 1891, ch 42, § 1; SDC 1939, § 12.0147.