Frost line depth in Sioux County, IA
How deep the ground freezes in Sioux County, IA
42 in. Dig to 43 in, just below the frost. Nearest NOAA station: Sioux Ctr 2 Se, 2.3 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.