From the Chicago Cross Cup website:
ROAD CLOSURE INFO FOR CARPENTERSVILLE
For those travelling on Rt. 31, it will be closed to through traffic on the day of the race between Route 72 (Higgens) and Route 62 (Algonquin Road). This means you may still be able to get through, but it may take a while. If you detour to Rt 25 , turn West (light) on Lake Marion Rd in Carpentersville, left on L.W. Besinger Dr, and a right on Maple Ave. Maple will take you directly to Carpenter Park.