Frost line depth in Kingsbury County, SD
How deep the ground freezes in Kingsbury County, SD
52 in. Dig to 53 in, just below the frost. Nearest NOAA station: De Smet, 2.8 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.