SDCL § 31-4-179: U.S. Highway 81 from Missouri River to Interstate Highway 29.

The state trunk highway system includes the following in Yankton, Hutchinson, McCook, Miner, Lake, Kingsbury, Hamlin, and Codington counties:

(1) From the center of the Missouri River Bridge south of Yankton northerly via Yankton and Salem to U.S. Highway 14 south of Arlington in the southwest quarter of section eighteen, township one hundred ten north, range fifty-two west;

(2) From a point on U.S. Highway 14 at Arlington near the west quarter corner of section six, township one hundred ten north, range fifty-two west, thence northerly via Arlington and Watertown to Interstate Highway 29 northeast of Watertown near the south quarter corner of section fifteen, township one hundred seventeen north, range fifty-two west.