35 ILCS 5/306: Allocation or apportionment of income by estates and trusts.

The items of income and deduction taken into account by an estate or trust in computing its base income for a taxable year shall be allocated or apportioned to this State to the extent provided by Sections 301 through 304 and, to the extent properly paid, credited or required to be distributed to beneficiaries for such taxable year, shall be deemed to have been so paid, credited or distributed pro rata.