605 ILCS 5/6-519
Whenever any refunding bonds are purchased and cancelled, as provided in Section 6-518, the taxes thereafter to be extended for payment of the principal of and 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, if a resolution has been adopted by the highway commissioner and the road district clerk of the road district finding these facts and a certified copy of the resolution has been filed with the county clerk specified in Section 6--516.
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 clerk of the road district, showing the bonds refunded and the tax to be abated.
605 ILCS 5/6-519