State Route 21 (SR 21) is a 85.9-mile-long (138.2 km) state highway that runs southeast-to-northwest through portions of Chatham, Effingham, Screven, and Jenkins counties in eastern part of the U.S. state of Georgia. The route connects Savannah to the Millen area, via Sylvania. The route is part of the Savannah River Parkway and is being considered for inclusion into Interstate 3.