SDCL § 7-1-11: Campbell County boundaries.

Beginning on the boundary line between the states of South Dakota and North Dakota where the tenth guide meridian west of the fifth principal meridian intersects the same, thence west and along said state line to the center of the main channel of the Missouri River; thence southerly and along the center of the main channel of said river to the sixth standard parallel north; thence east and along said sixth standard parallel to its intersection with the said tenth guide meridian; thence north and along said tenth guide meridian to the place of beginning.