
Any animals found in Chicago should be reported to the City of Chicago Animal Care and Control at (312) 744-5000.
Animal Care and Control will be able to assist you with the situation and help reunite the animal with its owner or otherwise find a good available space for it.
PAWS Chicago has good recommendations on how to handle Stray or Lost Pets at:
http://www.pawschicago.org/GivingUpYourPet/helpingalostanimal.htm
They also recommend visiting the Humane Society for additional information on "What to Do When You Find a Stray Dog or Cat".