What is the frost line in South Carolina?

In most of SC the frost line is 10 inches (0.25 meter) below grade. In the mountains of SC it's 20 inches/0.50 meters. See the related link below. EVENTUALLY they get to the frost lines. However, if you're putting in footings, you should check the International Building Code, IBC, I believe it calls for the bottom of the footing to be 12 inches below grade--- excepting the mountains.