Frost line depth in Keokuk County, IA
How deep the ground freezes in Keokuk County, IA
38 in. Dig to 38 in, just below the frost. Nearest NOAA station: Sigourney, 3.1 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.