65 ILCS 5/8-4-7
Whenever any refunding bonds are purchased or redeemed and cancelled, as provided in Section 8-4-6, the taxes thereafter to be extended for payment of the principal of and the interest on the remainder of the issue shall be reduced in an amount equal to the principal of and the interest that would have thereafter accrued upon the refunding bonds so cancelled. A resolution shall be adopted by the corporate authorities of the municipality finding these facts. A certified copy of this resolution shall be filed with the county clerk specified in Section 8-4-4. Whereupon the county clerk shall reduce and extend such tax levies in accordance therewith.
Whenever refunding bonds are issued, proper reduction of taxes, theretofore levied for the payment of the bonds refunded and next to be extended for collection, shall be made by the county clerk upon receipt of a certificate signed by the treasurer and the comptroller, if there is a comptroller, of the municipality, showing the bonds refunded and the tax to be abated.
65 ILCS 5/8-4-7