605 ILCS 5/10-306

The county board of each such county shall install and maintain a proper system of accounts, showing the receipts from the operation of the bridge and the application of the same, and the county board shall at least once a year cause such accounts to be properly audited by a certified public accountant and copies of such audit shall be filed in the office of the county clerk and shall be open for inspection at all proper times to any taxpayer, bondholder or other creditor of such county.