Frost line depth in Boundary County, ID
How deep the ground freezes in Boundary County, ID
25 in. Dig to 25 in, just below the frost. Nearest NOAA station: Bonners Ferry, 11.2 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.