The report found overtime was paid to more than a thousand employees who may have been ineligible.
The report says those employees work across 24 departments, including the Board of Elections, the Office of the City Clerk, and for the City Council.
Nearly a quarter of the money was paid to 18 employees, who received between $250,000 and $700,000 in overtime pay, over a five year period, the report said.
Several of the employees are with the fire department, the report showed.
ABC7 reached out to the Chicago Fire Department, but was told they had no comment.