Frost line depth in Cass County, MO
How deep the ground freezes in Cass County, MO
22 in. Dig to 22 in, just below the frost. Nearest NOAA station: Pleasant Hill Wfo, 12.3 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.