105 ILCS 5/19-24
Money received from the proceeds of taxes levied for payment of the principal of and interest upon refunding bonds shall be deposited in a special fund of the school district, designated as the "Refunding Bond and Interest Sinking Fund Account of ....". This fund shall be applied to the purchase or payment of refunding bonds and the interest thereon as provided in Sections 19--16 through 19--26.
If the money in this fund is not immediately necessary for the payment of refunding bonds or if refunding bonds can not be purchased before maturity, then, under the direction of the corporate authorities of the school district, the money may be invested by the treasurer of the school district in bonds or other interest bearing obligations of the United States or in bonds of the State of Illinois.
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 school district. The corporate authorities may sell these securities whenever necessary to obtain cash to meet bond and interest payments.
105 ILCS 5/19-24