Frost line depth in Douglas County, MN
How deep the ground freezes in Douglas County, MN
59 in. Dig to 59 in, just below the frost. Nearest NOAA station: Alexandria Muni Ap, 5.8 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.