South Dakota Highway 34 (SD 34) is a state route that runs parallel to Interstate 90 across the entire state of South Dakota. It begins at the Wyoming border west of Belle Fourche, as a continuation of Wyoming Highway 24 (WYO 24). The eastern terminus is at the Minnesota border east of Egan, or southwest of Airlie, Minnesota, where it continues as Minnesota State Highway 30 (MN 30). It is just over 419 miles (674 km) in length, making it the longest state highway in South Dakota.

Quick Facts Highway 34, Route information ...

Highway 34
Route of SD 34 (in red)
Route information
Maintained by SDDOT
Length	419.010 mi[1][2][3][4] (674.331 km)
Existed	1926–present
Tourist routes	Lewis and Clark Trail Native American Scenic Byway
Major junctions
West end	WYO 24 at Wyoming state line
Major intersections	US 85 at Belle Fourche I-90 / US 14 at Sturgis US 83 / US 14 at Pierre US 281 east of Wessington Springs US 81 at Madison I-29 south-east of Madison
East end	MN 30 at Minnesota state line
Location
Country	United States
State	South Dakota
Counties	Butte, Lawrence, Meade, Ziebach, Haakon, Stanley, Hughes, Hyde, Buffalo, Jerauld, Sanborn, Miner, Lake, Moody
Highway system
South Dakota State Trunk Highway System Interstate US State
← SD 32 → SD 35

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When first implemented in 1926, the western terminus was at South Dakota Highway 45 near Gann Valley. In the 1940s and early 1950s, a road was gradually built from Pierre to SD 45 via Fort Thompson, and SD 34 was extended west along it upon its completion. A further extension westward occurred in February 1961, when SD 34 absorbed the alignment of South Dakota Highway 24.^[5]

In the late 1960s, a portion of SD 34 (along with U.S. Highway 14) was upgraded as part of the construction of Interstate 90. The segment between Whitewood and Sturgis (exits 23 and 30) remains signed with I-90 and U.S. 14.

A 10-mile (16 km) segment of SD 34 in Sanborn County has been upgraded to 4 lanes. This is part of a 4-lane route from Huron to Mitchell via South Dakota Highway 37.

• List of state highways in South Dakota