70 ILCS 520/7.5
The issuance of bonds under this Act is deemed an essential public and governmental purpose. Interest on the bonds issued under this Act after the effective date of this amendatory Act of 1996 is exempt from taxation within this State.
For purposes of Section 250 of the Illinois Income Tax Act, the exemption of the interest from bonds granted under this Section 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.
70 ILCS 520/7.5