20 ILCS 3510/8
Bonds issued by the Authority under this Act, their transfer, the interest payable on them, and any income derived from them shall be exempt from taxation under the Illinois Income Tax Act, as now or hereafter amended, or from taxation by any political subdivision, municipal corporation or public agency of any kind of or within the State. For purposes of Section 250 of the Illinois Income Tax Act, the exemption of the income from bonds issued by the Authority shall terminate after all of the bonds have been paid. The amount of such income that shall be added and then subtracted on the Illinois income tax return of a taxpayer, pursuant to Section 203 of the Illinois Income Tax Act, from federal adjusted gross income or federal taxable income in computing Illinois base income shall be the interest net of any bond premium amortization.
20 ILCS 3510/8