Officer Oneta Sampson Carney was loading her car with her husband outside an Evergreen Park Sam's Club last year, when three men approached them, prosecutors previously said.
That's when they said two of the men offered to help the couple, while a third jumped in the driver's seat and drove off.
Prosecutors said Carney then fired her gun, hitting the pavement behind the car.
They said the men didn't show a gun or threaten the couple.
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No one was hurt.
Carney was charged with felony reckless discharge of a firearm, but was found not guilty in a one-day bench trial Tuesday.
Chicago's Civilian Office of Police Accountability was investigating the incident, and Carney was facing dismissal as of a May Chicago Police Board decision.
Sun-Times Media contributed to this report.