South Dakota Constitution
Article 1 - Name and Boundary.
§ 2 Boundaries of state.

§ 2. Boundaries of state. The boundaries of the state of South Dakota shall be as follows: Beginning at the point of intersection of the western boundary line of the state of Minnesota, with the northern boundary line of the state of Iowa and running thence northerly along the western boundary line of the state of Minnesota, to its intersection with the seventh standard parallel; thence west on the line of the seventh standard parallel produced due west to its intersection with the twenty-seventh meridian of longitude west from Washington; thence south on the twenty-seventh meridian of longitude west from Washington to its intersection with the northern boundary line of the state of Nebraska; thence easterly along the northern boundary line of the state of Nebraska to its intersection with the western boundary line of the state of Iowa; thence northerly along the western boundary line of the state of Iowa to its intersection with the northern boundary line of the state of Iowa; thence east along the northern boundary line of the state of Iowa to the place of beginning.