70 ILCS 1520/3
Money received from the proceeds of taxes levied for payment of principal of and interest upon such bonds shall be deposited in a special fund of such park district suitably designated for identification and such fund shall be faithfully applied to the payment of bonds and interest thereon for which such taxes were levied.
If such money is not immediately necessary for the payment of said bonds or if such bonds cannot be purchased before maturity then said money may be invested under the direction of the commissioners in bonds or other interest bearing obligations of the United States or bonds of the State of Illinois.
The maturity date of the invested securities shall be prior to the due date of the bonds for the payment of which said money was collected. Such securities may be sold when ordered by the commissioners if necessary to obtain cash to meet bond and interest payments.
Prior to the maturity of the bonds after setting aside a sum of money equal to the amount of interest that will accrue thereon within the next six months period from the time it is proposed to purchase and/or redeem any such bonds, or the commissioners may require that said sum of money may be equal to the amount of interest that will so accrue within the next twelve months' period, the treasurer of the park district shall use the money available from the proceeds of taxes levied for payment of the bonds, first in the purchase of such bonds at the lowest price obtainable, but not to exceed their par value and accrued interest after sealed tenders for their purchase shall have been advertised for as may be directed by the commissioners and thereafter such money shall be used by that official in calling such bonds for payment if, by their terms, they are subject to redemption.
Bonds called for payment and paid, or purchased, shall be marked paid and cancelled.
Whenever any bonds are purchased and/or redeemed and cancelled, the taxes thereafter to be extended for payment of interest shall be reduced in an amount equal to the interest that thereafter would have accrued upon such bonds so cancelled, and a resolution shall be adopted by the commissioners finding such facts and a certified copy thereof shall be filed in the office of the county clerk of Cook County whereupon it shall be the duty of such official to reduce and extend such tax levies in accordance therewith.
70 ILCS 1520/3