| State: | SD |
| Type: | SD |
| Route: | 43 |
| Section: | 163 |
| Map Notes: | Location of SD 43 (in red) |
| Length Mi: | 1.131 |
| Length Ref: | [1] |
| Established: | 1976 |
| Direction A: | South |
| Terminus A: | at the Nebraska state line south of Fairfax |
| Direction B: | North |
| Terminus B: | near Fairfax |
| Counties: | Gregory |
| Previous Type: | SD |
| Previous Route: | 42 |
| Next Type: | SD |
| Next Route: | 44 |
South Dakota Highway 43 (SD 43) is a 1.131adj=midNaNadj=mid state highway that exists entirely in the southern part of Gregory County in the southern part of the U.S. state of South Dakota. It begins as an extension of Nebraska Highway 11 (N-11) at the Nebraska state line south of Fairfax. It travels northwest to an intersection with U.S. Route 18 (US 18) south-southwest of the town.
SD 43 begins at the Nebraska state line as a continuation of N-11. It travels northwest for just over 1miles before meeting its northern terminus at an intersection with US 18. The highway does not travel through any populated areas, but rather serves as a connector route between N-11 and US 18.[2]
The first road designated as SD 43 was around 1932, in Platte. It traveled east before heading south to travel through Geddes, ending at US 18 west of Lake Andes. This segment, previously part of SD 45, was given a separate number when SD 45 was rerouted south from Platte. By 1935, it was extended to the north and west, assuming the routing of SD 47 when the latter highway was relocated west of the Missouri River; its northern terminus was at the intersection of US 16 in Pukwana (in Brule County). The number was removed around 1940, when SD 50 was extended northwest from its previous terminus near Ravinia (east of Lake Andes).
The present day SD 43 was initially a segment of US 281. That highway's entrance into South Dakota was moved about 9miles to the east, by 1962. The old alignment was unnumbered until 1976, when it given its current assignment.