The 25-inch alligator was found at O'Hare in November after surveillance photos showed it with a woman on the CTA's Blue Line train.
Alexis Prokopchuk, 29, of Oakbrook Terrace, is charged with animal cruelty and reckless conduct on Wednesday. Both are misdemeanors, prosecutors said.
In a report, police say Prokopchuk told arresting officers she took the baby gator from a friend who was originally going to flush the alligator down the toilet, but forgot it at the airport because she was "on crack cocaine and heroin," according to "The Chicago Tribune".
Someone spotted the alligator under an escalator in the lower level of terminal three at the airport and called officials. A reptile expert said the alligator was in poor health when discovered. The alligator was transferred into the care of the Chicago Herpetological Society, and "is still in quarantine in an isolation tank," according to CHS Vice President Jason Hood. Nine days after it was found at O'Hare, the alligator started eating again. It remains skittish, but is expected to make "a nearly full recovery."