Frost line depth in Knox County, MO
How deep the ground freezes in Knox County, MO
28 in. Dig to 28 in, just below the frost. Nearest NOAA station: Steffenville, 17.9 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.