70 ILCS 2605/5.8
No contract shall hereafter be made, or expense or liability incurred by the said board of trustees, or any member or committee thereof, or by any person or persons, for or in its behalf notwithstanding the expenditure may have been ordered by the said board of trustees, unless an appropriation therefor shall have been previously made by said board in the manner aforesaid. No officer, head of a department, or commission shall, during a budget year, expend or contract to expend any money or incur any liability, or enter into any contract, which, by its terms, involves the expenditure of money for any of the purposes for which provision is made in the appropriation ordinance in excess of the amounts appropriated in said ordinance. Any contract, verbal, or written, made in violation of this section shall be null and void as to the district, and no moneys shall be paid thereon; provided, however, that nothing herein contained shall prevent the making of contracts for the lawful purposes of said district, the terms of which contracts may be for periods of more than one year, but any contract so made shall be executory only for the amounts for which the said district is lawfully liable in succeeding budget years.
The books of account of the district shall be so kept that it shall be possible to determine at any time the exact condition of each of the separate amounts appropriated. One set of budgetary books shall be known as the appropriation record of the district and shall be kept in such manner as to indicate for each amount appropriated at all times at least such information as the amount originally appropriated, transfers during the year, encumbrances, disbursements, and unencumbered balances. Every obligation of the district for purchase orders, contracts, or other commitments shall be reported in the appropriation record irrespective of the contemplated date of delivery, receipt, or payment.
70 ILCS 2605/5.8