Frost line depth in Billings County, ND
How deep the ground freezes in Billings County, ND
51 in. Dig to 52 in, just below the frost. Nearest NOAA station: Medora 7 E, 7.8 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.