Frost line depth in Door County, WI
How deep the ground freezes in Door County, WI
43 in. Dig to 43 in, just below the frost. Nearest NOAA station: Ephraim 1ne-Wwtp, 7.4 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.