Frost line depth in Clay County, IA
How deep the ground freezes in Clay County, IA
47 in. Dig to 47 in, just below the frost. Nearest NOAA station: Spencer 1 N, 5.8 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.