Frost line depth in Butler County, IA
How deep the ground freezes in Butler County, IA
46 in. Dig to 46 in, just below the frost. Nearest NOAA station: Allison, 1.7 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.