Frost line depth in Kendall County, IL
How deep the ground freezes in Kendall County, IL
35 in. Dig to 35 in, just below the frost. Nearest NOAA station: Chicago Aurora Muni Ap, 12.8 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.