Frost line depth in Tulsa County, OK
How deep the ground freezes in Tulsa County, OK
12 in. Dig to 13 in, just below the frost. Nearest NOAA station: Tulsa R L Jones Jr Ap, 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.