There is no Indian Consulate in Illinois!
Since Illinois comes under the jurisdiction of Consulate at Chicago, the nearest Indian Consulate you should visit is located at Chicago at the below address
Chicago Consulate Address
Consulate General of India,
55 North City Front Plaza Drive, NBC Tower Building,
Suite No. 850,
Chicago, IL 60611
Helpline Tel: 312-595-0405
See more about Chicago Consulate at here – http://passportindiaguide.com/indian-consulate-in-chicago/