40 ILCS 5/1-104.3

Notwithstanding any other provision of this Code to the contrary, beginning on the effective date of this amendatory Act of the 95th General Assembly, legally adopted children shall be entitled to the same benefits as other children, and no child's or survivor's benefit shall be disallowed because the child is an adopted child. The provisions of this Section apply without regard to whether the employee or member was in service on or after the date of the adoption of the child.