Frost line depth in Marquette County, MI
How deep the ground freezes in Marquette County, MI
58 in. Dig to 58 in, just below the frost. Nearest NOAA station: Marquette, 8.8 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.