40 ILCS 5/15-190
If a person is under legal disability when any right or privilege accrues to him or her under this Article, a guardian may be appointed pursuant to law, and may, on behalf of such person, claim and exercise any such right or privilege with the same force and effect as if the person had not been under a legal disability and had claimed or exercised such right or privilege.
If a person's application for benefits or a physician's certificate on file with the board shows that the person is under a legal disability, the benefits payable under this Article may be paid (1) directly to the person under legal disability, (2) to any person who has legally qualified and is acting as guardian of the property of the person under legal disability, (3) to either parent of the person under legal disability or any adult person with whom the person under legal disability may at the time be living, provided only that such parent or adult person to whom any amount is to be paid shall have advised the board in writing that such amount will be held or used for the benefit of the person under legal disability, or (4) to the trustee of any trust created for the sole benefit of the person under legal disability while that person is living, provided only that the trustee of such trust to whom any amount is to be paid shall have advised the board in writing that such amount will be held or used for the benefit of the person under legal disability. The system shall not be required to determine the validity of the trust or any of the terms thereof. The representation of the trustee that the trust meets the requirements of this Section shall be conclusive as to the system. The written receipt of the person under legal disability or the other person who receives such payment shall be an absolute discharge of the system's liability in respect of the amount so paid.
40 ILCS 5/15-190