SDCL § 7-1-64: Union County boundaries.

Beginning at a point where the township line between townships ninety-five and ninety-six north intersects the boundary line between the states of South Dakota and Iowa, thence west and along the township line between townships ninety-five and ninety-six north, to the northwest corner of township ninety-five, range fifty, west of the fifth principal meridian; thence south and along the range line between ranges fifty and fifty-one west, to the boundary line between the states of South Dakota and Nebraska; thence southeasterly and along said last mentioned state line to its intersection with the boundary line between the states of South Dakota and Iowa; thence northerly and along the boundary between the states of South Dakota and Iowa, to the place of beginning.