South Carolina Highway 421 (SC 421) is a state highway in the U.S. state of South Carolina. It is an alternate route to U.S. Route 1 (US 1) and US 78 between North Augusta and Aiken. Route description SC 421 begins where it splits off from US 1/US 78 (Jefferson Davis Highway) southwest of Clearwater; it immediately connects with US 278/SC 125 (Atomic Road). Heading northeast, it parallels US 1/US 78 to its south, going through the towns of Clearwater, Burnettown, Langley, Gloverville and Warrenville. Upon entering Aiken, it reconnects with US 1/US 78. A majority of the highway is four-lanes that travels a total of . History SC 421 was established by 1952 as a renumbering of US 1/US 78, which was realigned onto new four-lane routing just north of it. The route has remained unchanged since inception. Major intersections See also References External links SC 421 at Virginia Highways' South Carolina Highways Annex 421 Transportation in Aiken County, South Carolina Aiken, South Carolina U.S. Route 1 U.S. Route 78