SDCL § 7-1-67: Yankton County boundaries.

Beginning at the northeast corner of township ninety-six north of range fifty-four west of the fifth principal meridian, thence west and along the township line between townships ninety-six and ninety-seven to the northwest corner of township ninety-six, north of range fifty-seven, west; thence south and along the range line between ranges fifty-seven and fifty-eight west, as extended, to its intersection with the boundary line between the states of South Dakota and Nebraska; thence easterly and along said state line to the range line between ranges fifty-three and fifty-four, as extended; thence north and along said range line to the place of beginning.