Frost line depth in Tarrant County, TX
How deep the ground freezes in Tarrant County, TX
7 in. Dig to 12 in, the 12 in code minimum. Nearest NOAA station: Ft Worth Wsfo, 4.3 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.