All of the below are within an hour of Chicago, I didn't mention Palwaukee, or some other northside airports.
Dupage (tower):
Illinois Aviation
Travel Express Air
Aurora (tower):
Lumanair
Bolingbrook Clow Airport:
A&M Aviation
Midway Airport (hehe tower):
Aviation Professionals (also at Gary)
Midway Aviators
Joliet:
J.F. Aviation
Morris:
Blue Sky Aero
New Lenox:
Not sure of name, they have a Decathlon and 3 99' 172s
Lansing:
Associated Air
Gary (tower):
Aviation Professionals (also at Midway)