Frost line depth in Harding County, SD
How deep the ground freezes in Harding County, SD
44 in. Dig to 45 in, just below the frost. Nearest NOAA station: Buffalo Asos, 3.5 mi.
Your building department sets the legal frost line depth (IRC Table R301.2(1)); footings must go below it (R403.1.4.1). Call them before you dig.