The county of Custer is bounded as follows: Commencing at the southeast corner of township thirteen, north, of range seventeen, west, of the sixth principal meridian; thence north to the northeast corner of township twenty, north, of range seventeen, west; thence west to the northwest corner of township twenty, north, of range twenty-five, west; thence south to the southwest corner of township thirteen, north, of range twenty-five, west; thence east to the place of beginning.