Frost line depth in Itasca County, MN
How deep the ground freezes in Itasca County, MN
71 in. Dig to 71 in, just below the frost. Nearest NOAA station: Marcell 5ne, 9.9 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.