The female gorilla, yet to be named, was born Wednesday, the Chicago Tribune reported.
"[She] appears to be doing well," an e-mail from the zoo said.
The mother is Bana, 15, and a silverback gorilla, 22 is the father, the release said.
"[The silverback] seems proud of his new offspring and has stayed protectively close to mother and baby," it said.
The zoo's Regenstein Center for African Apes has been closed to the public since the birth to give the gorillas time to adjust to the newborn.
The building will reopen at 10 a.m. Tuesday.
The baby is the 49th gorilla born at the zoo, the release said.