Frost line depth in Jefferson County, ID
How deep the ground freezes in Jefferson County, ID
46 in. Dig to 46 in, just below the frost. Nearest NOAA station: Hamer 4 Nw, 12 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.