Frost line depth in Pierce County, WI
How deep the ground freezes in Pierce County, WI
57 in. Dig to 57 in, just below the frost. Nearest NOAA station: Ellsworth 1e, 1.6 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.