The abduction and theft happened around 12:40 a.m. Thursday in western suburban Bensenville, the Chicago Tribune reported.
The girl's mother left her in the car while she went into an apartment building, police said.
"A subject walked out the foyer and walked directly to her car parked directly in front of the foyer ... and drove away," Bensenville Police chief Frank Kosman said.
The car was found hours later abandoned about a mile away, Kosman said.
The girl appeared safe and unharmed, police said.
Kosman said police are looking for the suspect and do not believe he knew there was a child in the backseat of the car.