Frost line depth in Clay County, MO
How deep the ground freezes in Clay County, MO
24 in. Dig to 25 in, just below the frost. Nearest NOAA station: Kearney 3e, 6.1 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.