Frost line depth in Buchanan County, IA
How deep the ground freezes in Buchanan County, IA
44 in. Dig to 44 in, just below the frost. Nearest NOAA station: Independence #1, 4.4 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.