Frost line depth in Muskegon County, MI
How deep the ground freezes in Muskegon County, MI
33 in. Dig to 33 in, just below the frost. Nearest NOAA station: Montague 4 Nw, 2.3 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.