Frost line depth in Ozaukee County, WI
How deep the ground freezes in Ozaukee County, WI
43 in. Dig to 43 in, just below the frost. Nearest NOAA station: Belgium Wwtp, 0.9 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.