Frost line depth in Sac County, IA
How deep the ground freezes in Sac County, IA
45 in. Dig to 45 in, just below the frost. Nearest NOAA station: Sac City, 6.9 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.