S.D. Codified Laws § 7-1-65
Beginning at the northeast corner of township one hundred twenty-four north of range seventy-four, west of the fifth principal meridian, thence west and along the sixth standard parallel north, to the center of the main channel of the Missouri River; thence southerly and down the center of the main channel of the Missouri River to its intersection with the fifth standard parallel, north, as extended; thence east and along the township line between townships one hundred twenty and one hundred twenty-one north, to the southeast corner of township one hundred twenty-one north of range seventy-four, west of the fifth principal meridian; thence north and along the range line between ranges seventy-three and seventy-four west, to the place of beginning.
SDCL 7-1-65