Frost line depth in Kane County, IL
How deep the ground freezes in Kane County, IL
33 in. Dig to 34 in, just below the frost. Nearest NOAA station: West Chicago Dupage Ap, 9.5 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.