20 ILCS 3501/820-60
The exercise of powers granted in this Article is in all respects for the benefit of the people of Illinois and in consideration thereof the bonds issued pursuant to the aforementioned Sections and the income therefrom shall be free from all taxation by the State or its political subdivisions, except for estate, transfer and inheritance taxes. For purposes of Section 250 of the Illinois Income Tax Act, the exemption of the income from bonds issued under the aforementioned Sections 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 3501/820-60