Frost line depth in Macoupin County, IL
How deep the ground freezes in Macoupin County, IL
24 in. Dig to 24 in, just below the frost. Nearest NOAA station: Carlinville, 3.4 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.