Chicago code is at:
http://www.amlegal.com/library/il/chicago.shtml

Go to 4-60-130, at the end of a-2, it says:

The holder of an airport pushcart liquor license or a consumption on the premises license for an establishment located within “authorized areas” of “O'Hare” or “Midway”, as those terms are defined in Section 4-60-077, may sell or permit to be sold alcoholic liquor at any time within such authorized areas, subject to such time restrictions as the commissioner of aviation may set by rule.

In 4-60-077, authorized areas is defined as past the security checkpoint.