South Dakota Highway 15

Highway 15
Route of SD 15 (in red)
Route information
Defined by SDCL §31-4-137
Maintained by SDDOT
Length:	79.430 mi (127.830 km)
Existed:	1926 (approx.) – present
Major junctions
South end:	SD 28 west of Toronto
North end:	I-29 west of Wilmot
Location
Counties:	Grant, Deuel
Highway system
South Dakota Highways Interstate U.S. State ← US 14A SD 16 →

South Dakota Highway 15 is a state route that largely runs north to south across northeastern South Dakota. The northern terminus is at the junction with Interstate 29 west of Wilmot (exit 213) and the southern terminus is at I-29 west of Toronto (exit 150). It is 78 miles (129 kilometers) in length.

The route of SD 15 is defined in South Dakota Codified Laws § 31-4-137.[1]

South Dakota 15, when designated in the mid-1920s, ran north to south across the entire state, on the road known as the King of Trails. The extension of U.S. Highway 77 in 1930 largely replaced the numbering of SD 15, from Milbank to Sioux City. The northern portion of the route, from U.S. Highway 12 to the North Dakota border north of Claire City, remained in place.

In the early 1950s, changes were made to the southern end. SD 15 was rerouted so the south end was at Milbank; it then went north to Hartford Beach, then west through Wilmot to U.S. Highway 81, before heading north again. The old alignment from Wilmot to U.S. 12 was designated at South Dakota Highway 15A.

In 1976, the segment of SD 15 from the North Dakota border to Claire City was made part of a realigned South Dakota Highway 25, and the segment from Claire City to U.S. 81 near Claire City was designated as South Dakota Highway 106. At that point, the northern terminus was located at U.S. 81 west of Wilmot.