Are rattlesnakes found in South Carolina?

Yes there are a few types of Rattlesnakes in the South Carolina region. Copperhead (Agkistrodon contortrix) - Venomous

Cottonmouth/Water Moccasin (Agkistrodon piscivorus) - Venomous

Eastern Diamondback Rattlesnake (Crotalus adamanteus) - Venomous

Canebrake/Timber Rattlesnake (Crotalus horridus) - Venomous

Pigmy Rattlesnake (Sistrurus miliarius)-venomous

The above answer is basically correct, but although cottonmouths and copperheads are pit vipers like rattlesnakes, they are species in their own right, and not rattlesnakes.