Illinois Statutes Chapter 35. Revenue § 405/3. Illinois estate tax

(a) Imposition of Tax. An Illinois estate tax is imposed on every taxable transfer involving transferred property having a tax situs within the State of Illinois.

(b) Amount of tax. On estates of persons dying before January 1, 2003, the amount of the Illinois estate tax shall be the state tax credit, as defined in Section 2 of this Act, with respect to the taxable transfer reduced by the lesser of:

(c) On estates of persons dying on or after January 1, 2003, the amount of the Illinois estate tax shall be the state tax credit, as defined in Section 2 of this Act, reduced by the amount determined by multiplying the state tax credit with respect to the taxable transfer by the percentage which the gross value of the transferred property not having a tax situs in Illinois bears to the gross value of the total transferred property.