The body was found in the Logan Square neighborhood in the 2700-block of North Hamlin. Police are investigating the infant's death as a homicide.
Neighbors have set up candles and stuffed animals as a memorial in the gangway where they found the baby curled up and wrapped in a plastic bag. Police say he appeared to be full term and still had the placenta attached.
Neighbor Andrea Vazquez ran to see the baby after a man doing work in her house called for help Saturday morning.
"He seen a baby there in the plastic bag, so he went inside right away, called us to come outside and see the baby. We came outside and right away called the police," said Vasquez.
Vazquez says she believes the baby's body was still warm. She believes whoever left the newborn here did so overnight, apparently shortly after giving birth. For the mother of two, it's hard to believe.
"It's just sad, real sad. How can a woman do that to her own child? Just put him in the plastic bag and put him over here?" said Vasquez.
Police questioned people in the neighborhood but they have yet to find the mother.
The house next door has security cameras, but they apparently failed to get a picture of whoever abandoned the baby.
"Just knock on the door, we could have come outside and helped the little baby," said Vasquez.
Authorities said it is an especially senseless tragedy. Had the mother left the infant at a medical facility, fire station or police station, she would have faced no questions under Illinois' Safe Haven law.
Now, however, the mother could faced murder charges.