105 ILCS 5/34-70
If the proceeds of the refunding bonds authorized by Section 34--65 have been used for the payment of any outstanding bonds of the board, or the refunding bonds have been exchanged for outstanding bonds, and thereafter any portion of the respective taxes levied for the purpose of paying the principal of and interest on the outstanding bonds so paid or exchanged is collected, the money so received shall be placed in the bond and interest sinking fund of the board and used for the purpose of paying the principal of and interest on the refunding bonds issued under Section 34--65 and the taxes thereafter to be extended to pay the refunding bonds shall be reduced by that amount by the county clerk upon receipt of a certified copy of a resolution which must be adopted by the board directing such reduction. A certified copy of the resolution shall be filed with the county clerk of the county, and it shall thereupon be the duty of such official to reduce and extend the tax levy in accordance with the terms of the resolution.
105 ILCS 5/34-70