Frost line depth in Mills County, TX
How deep the ground freezes in Mills County, TX
6 in. Dig to 12 in, the 12 in code minimum. Nearest NOAA station: Goldthwaite 1 Wsw, 3.8 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.