A Dolton spokesperson said witnesses told them the shooting happened as a balloon release was about to take place at 151st and Cornell.
A suspect, concealed in nearby bushes, stepped out and opened fire.
Three people were shot and taken to local hospitals.
The spokesperson said the victims appear to have non-life-threatening injuries.
Detectives are on the scene, and no one is in custody.
Further information was not immediately available.
This is a developing story. Check back with ABC7 for updates.