SDCL § 7-1-24: Fall River County boundaries.

Beginning at a point where the one hundred third meridian of west longitude intersects the boundary line between townships six and seven, south Black Hills base line, thence west and along said township line to the boundary line between the states of South Dakota and Wyoming; thence south and along said state line to its intersection with the boundary line between the states of South Dakota and Nebraska; thence east and along said state line to its intersection with said one hundred third meridian; thence north along said meridian to the place of beginning.