Frost line depth in Washington County, TN
How deep the ground freezes in Washington County, TN
16 in. Dig to 16 in, just below the frost. Nearest NOAA station: Erwin 1 W, 11.3 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.