It happened around 10:13 p.m. Saturday at the Taco Bell in the West Rogers Park neighborhood's 3500 block of West Devon Avenue near suburban Lincolnwood, police said.
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Witnesses said two people were arguing when one pulled out a gun and shot the other.
The victim, a 37-year-old man, was hit in the shoulder and taken to St. Francis Hospital in fair condition, police said. Police said the person who fired shots fled the scene.
No arrests have been made and Area Five detectives are investigating.