But County Board President Toni Preckwinkle said Friday that the problem she inherited renews her "commitment to transparency and accountability."
Errors included duplicate journal entries for $66 million in sales tax revenue and $24 million in cigarette taxes.
The Chicago Sun-Times says new reporting practices currently are in place, and the employee responsible for the error, Faisal Abbasi, was fired earlier this year.
Abbasi said he doesn't know whether he's responsible for the double entry.
Deloitte and Touche, the firm that audited the county's 2009 records, could not be reached for comment.