Frost line depth in Greene County, IL
How deep the ground freezes in Greene County, IL
25 in. Dig to 26 in, just below the frost. Nearest NOAA station: White Hall 1 E, 5.9 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.