The shooting happened just before 12:30 p.m., North Riverside Fire Chief John Kiser said.
North Riverside police responded to the shooting inside the lower level of the mall's southern end and found a man in his 20s with a gunshot wound.
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The man was taken to Loyola University Medical Center. Officials did not release his condition as of late Sunday afternoon.
No information was immediately provided about the circumstances surrounding the shooting, but police said no one was in custody.
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The mall is closed for the rest of Sunday, but is expected to reopen Monday, the mall's spokeswoman Cheryl Georgas said.
It was evacuated after the shooting occurred.
Sunday's shooting marks the second such incident at the North Riverside Park Mall in less than a month. Earlier in June, a 22-year-old man was shot to death behind the mall's Olive Garden restaurant.
Sun-Times Media contributed to this report.