Frost line depth in Clarke County, IA
How deep the ground freezes in Clarke County, IA
36 in. Dig to 36 in, just below the frost. Nearest NOAA station: Osceola, 2 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.