Frost line depth in Roosevelt County, MT
How deep the ground freezes in Roosevelt County, MT
62 in. Dig to 63 in, just below the frost. Nearest NOAA station: Wolf Point 29 Ene, 5.2 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.