South Dakota Highway 20

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Highway 20
Map of South Dakota with SD 20 in red
Route information
Maintained by SDDOT
Length	385.079 mi[1][2][3] (619.725 km)
Existed	c. 1930[citation needed]–present
Tourist routes	Lewis and Clark Trail Native American Scenic Byway
Western segment
Length	346.065 mi[1][2][3] (556.938 km)
West end	Montana state line near Camp Crook
Major intersections	US 85 from Buffalo to south of Buffalo US 12 from near Mobridge to south of Selby US 83 from northwest of Selby to southwest of Lowry US 281 in Mellette
East end	US 212 in Watertown
Eastern segment
Length	39.014 mi[3] (62.787 km)
West end	CR 11 (455th Avenue) west of South Shore
Major intersections	I-29 / US 81 west of South Shore SD 15 from east of Stockholm to near Revillo
East end	MN 40 at the Minnesota state line near Revillo
Location
Country	United States
State	South Dakota
Counties	Harding Perkins Ziebach Dewey Corson Walworth Potter Faulk Spink Clark Codington Grant
Highway system
South Dakota State Trunk Highway System Interstate US State
← SD 19 → SD 21

South Dakota Highway 20 (SD 20) is a 385.079-mile (619.725 km) state highway in northern South Dakota, United States, that connects the Montana state line, west-southwest of Camp Crook, with the Minnesota state line, east-southeast of Revillo, via Buffalo, Bison, Timber Lake, Mobridge, Selby, and Watertown. From Mobridge to the Walworth–Potter county line, this highway is part of the Lewis and Clark Trail. From about Timber Lake to just west of Mobridge, this highway is part of the Native American Scenic Byway. From the Montana state line to Camp Crook, the highway is a dirt road.

SD 20 is composed of two disconnected segments. The longer western segment extends 346 miles (557 km) from Montana to Watertown. The much-shorter eastern segment extends 39 miles (63 km) from west of South Shore to Minnesota. However, the South Dakota Department of Transportation previously indicated that SD 20 followed US 212, US 81, and Interstate 29 (I-29) between the two segments.^[3]

SD 20 originally extended from SD 45 west of Cresbard to Watertown. It was extended west to U.S. Route 83, southwest of Lowry. Later, it was extended to its current eastern terminus. Later still, it was extended to its current western terminus, replacing what had been SD 8 (and later SD 18).