S.D. Codified Laws § 7-1-55
Beginning at a point where the boundary line between the states of South Dakota and North Dakota intersects the boundary line between the states of South Dakota and Minnesota, thence west and along said state line between the states of South Dakota and North Dakota to the range line between ranges fifty-two and fifty-three west of the fifth principal meridian, according to the survey of the former Sisseton and Wahpeton Indian Reservation; thence south and along said range line to the township line between townships one hundred twenty-one and one hundred twenty-two north of said survey; thence east and along said township line to the easterly boundary of said former Indian reservation; thence northeasterly along the boundary line of said former Indian reservation to the township line between townships one hundred twenty-one and one hundred twenty-two north, outside of said Indian reservation; thence east on said township line to the boundary line between the states of South Dakota and Minnesota; thence northerly and along said state line to the place of beginning.
SDCL 7-1-55