Frost line depth in Montcalm County, MI
How deep the ground freezes in Montcalm County, MI
38 in. Dig to 38 in, just below the frost. Nearest NOAA station: Greenville 2 Nne, 8.9 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.