Frost line depth in Burleigh County, ND
How deep the ground freezes in Burleigh County, ND
57 in. Dig to 57 in, just below the frost. Nearest NOAA station: Bismarck 2.4 Nnw, 18.4 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.