U.S. Route 12 in South Dakota

U.S. Highway 12 (US 12) is a part of the United States Numbered Highway System that travels from Aberdeen, Washington, to Detroit, Michigan. In the state of South Dakota, US 12 extends from the North Dakota border east to the Minnesota border.

Route description
US 12 enters South Dakota from North Dakota as a rural two-lane highway about 10 mi west-northwest of Lemmon before entering the Standing Rock Indian Reservation. For approximately the next 70 mi, US 12 runs parallel to the border of North Dakota, sometimes within less than. At Walker, US 12 heads southeast for 37 mi, where it crosses the Missouri River at Mobridge, exiting the reservation. From there, it continues east for 18 mi, until it meets with US 83 near Selby. It overlaps US 83 for 7 mi. After leaving US 83, it turns due east and spends about 80 mi as a rural two-lane highway again. A few miles before reaching Aberdeen, it becomes an at-grade expressway. After the junction with US 281, it goes back to being two lanes for a few miles through Aberdeen and past Aberdeen Regional Airport, before once again becoming a four-lane expressway, until 2 mi before Waubay. East of Waubay it becomes again an at-grade expressway until it meets with I-29 near Summit. The speed limit from Aberdeen to I-29 is 70 mph except through the communities of Groton, Webster, and Waubay. From there, it heads southeast 22 mi until Milbank. At Milbank, it continues east for 12 mi, until it crosses into Minnesota at Big Stone City, just south of Big Stone Lake.

The South Dakota section of US 12 is legally defined at South Dakota Codified Laws § 31-4-132.