South Carolina Highway 121 (SC 121) is a 134.200-mile (215.974 km) major state highway that travels north and south in central parts of the U.S. state of South Carolina. The highway is actually part of a long multi-state highway that also exists in Florida and Georgia, as Florida State Road 121 and Georgia State Route 121, respectively. Some see it as a de facto auxiliary route from U.S. Route 21 (US 21) in Rock Hill. Efforts to have the road upgraded to such status have failed however.