Frost line depth in Oregon County, MO
How deep the ground freezes in Oregon County, MO
19 in. Dig to 19 in, just below the frost. Nearest NOAA station: Alton, 0.5 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.