65 ILCS 5/8-4-8
Money which becomes available from taxes that were levied for prior years for payment of bonds or interest coupons that were paid or refunded before these taxes were collected, after payment of all warrants that may have been issued in anticipation of these taxes, shall be placed in the sinking fund account provided in this section. It shall be used to purchase, call for payment, or to pay at maturity refunding bonds and interest thereon as provided in Sections 8-4-3 through 8-4-9.
Money received from the proceeds of taxes levied for the payment of the principal of and interest upon refunding bonds shall be deposited in a special fund of the municipality. It shall be designated as the "Refunding Bond and Interest Sinking Fund Account of ....." This fund shall be faithfully applied to the purchase or payment of refunding bonds and the interest thereon as provided in Sections 8-4-3 through 8-4-9.
If the money in this fund is not immediately necessary for the payment or redemption of refunding bonds or if refunding bonds can not be purchased before maturity, then, under the direction of the corporate authorities of the municipality, the money may be invested by the treasurer and the comptroller, if there is a comptroller, of the municipality, in bonds or other interest bearing obligations of the United States or in bonds of the State of Illinois or in general obligation bonds of the issuing municipality.
The maturity date of the securities in which this money is invested shall be prior to the due date of any issue of refunding bonds of the investing municipality. The corporate authorities may sell these securities whenever necessary to obtain cash to meet bond and interest payments.
65 ILCS 5/8-4-8