The town's mayor was at the business and had minor injuries while seeking safety.
The shooting incident happened in the 13000 block of South Claire Boulevard in Robbins, Illinois, the Cook County Medical Examiner's Office said.
A 29-year-old man was pronounced dead around 1 a.m. Saturday, the medical examiner said. His death was a ruled a homicide from multiple gunshot wounds at the location.
Robbins officials later provided an update to ABC7, saying a "masked gunman entered the restaurant and opened fire toward an intended target. A contracted security officer with the restaurant intervened shooting the offender who was later pronounced dead."
Robbins Mayor Darren Bryant was at the restaurant and was hospitalized with a minor injury, officials said. He was not the intended target of the gunman.
Cook County Sheriff's Police Detectives said they were requested by Robbins police on Saturday to help investigate the shooting. The sheriff's police confirmed a 29-year-old man and a 34-year-old man were hospitalized with minor injuries after the shooting incident.
The deceased suspect was identified by the Cook County Sheriff's Department as 29-year-old Marquelle Rose of Chicago.
A spokesperson for the village of Robbins provided the following full statement Sunday:
"A shooting occurred last evening at Harold's Chicken Restaurant in Robbins. A masked gunman entered the restaurant and opened fire toward an intended target. A contracted security officer with the restaurant intervened shooting the offender who was later pronounced dead.
"Robbins Mayor Darren Bryant was inside the restaurant but was not the intended target. Mayor Bryant sustained a minor injury while seeking safety with other patrons, he was treated at a local hospital, and released within an hour.
"This incident is not indicative of the Robbins community, as the individuals involved were not residents of Robbins. This isolated act of violence does not reflect the people, families, or spirit of our community.
"The Cook County Sheriff's Department is investigating the incident."