Section 35 ILCS 405/4 - Illinois generation-skipping transfer tax(a) Imposition of tax. An Illinois generation-skipping transfer tax is imposed on every taxable transfer resulting in federal generation-skipping transfer tax involving transferred property having a tax situs within the State of Illinois.(b) Amount of tax. The amount of the Illinois generation-skipping transfer tax shall be the maximum state tax credit allowable with respect to the taxable transfer, reduced by the lesser of: (1) the amount of the state tax credit paid to any other state or states; and(2) the amount determined by multiplying the maximum state tax credit allowable 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.