Depends on what you want for thin. If you want a NY style thin, one of the absolute best I've had is Gigio's in downtown Evanston. Counter service place that sells by the slice or whole as well as having decent Italian Beef and burgers.
Gigio's
1001 Davis St.
Evanston, IL
847-328-0090
For a thin crispy crust, Vito and Nick on the south side is excellent.
Vito and Nick Pizzeria
8435 S. Pulaski
Chicago, IL
773-735-2050