105 ILCS 5/19-29
In computing the debt incurring power of any school district where there has been included in any such school district only a part of any former school district which at the time of such inclusion has outstanding bonded indebtedness, a proportionate amount of such bonded indebtedness shall be chargeable to such school district based upon the ratio that the assessed valuation of taxable property as equalized and determined by the Department of Revenue in that part of the territory of such former school district that has been included in any such school district bears to the total assessed valuation of the former school district as equalized and determined by the Department of Revenue for the year in which the change occurred, and the proportionate amount of such bonded indebtedness shall be chargeable against such school district in determining its debt incurring power.
105 ILCS 5/19-29