Frost line depth in Kent County, MI
How deep the ground freezes in Kent County, MI
26 in. Dig to 27 in, just below the frost. Nearest NOAA station: E Grand Rapids, 7.3 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.