South Dakota Highway 21

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Highway 21
Map of South Dakota with SD 21 in red
Route information
Maintained by SDDOT
Length	9.470 mi[1] (15.240 km)
Existed	1926[citation needed]–present
Major junctions
South end	SD 28 west of Lake Norden
North end	US 81 east of Hayti
Location
Country	United States
State	South Dakota
Counties	Hamlin
Highway system
South Dakota State Trunk Highway System Interstate US State
← SD 20 → SD 22

South Dakota Highway 21 (SD 21) is a 9.470-mile (15.240 km) state highway in south-central Hamlin Countym South Dakota, that connects Lake Norden and Hayti.

SD 21 originally extended from the Nebraska state line to the North Dakota state line, completely concurrent with U.S. Route 81 (US 81). By the mid-1930s, only the current part of the highway remained.