35 ILCS 110/18
As soon as practicable after a claim for credit or refund is filed, the Department shall examine the same and determine the amount of credit or refund to which the claimant or the claimant's legal representative, in the event that the claimant shall have died or become a person under legal disability, is entitled and shall, by its Notice of Tentative Determination of Claim, notify the claimant or his legal representative of such determination, which determination shall be prima facie correct. Proof of such determination by the Department may be made at any hearing before the Department or the Illinois Independent Tax Tribunal, as applicable, or in any legal proceeding by a reproduced copy of the Department's record relating thereto, in the name of the Department under the certificate of the Director of Revenue. Such reproduced copy shall, without further proof, be admitted into evidence before the Department or in any legal proceeding and shall be prima facie proof of the correctness of the Department's determination, as shown therein. If such claimant, or the legal representative of a deceased claimant or a claimant who is a person under legal disability, shall, within 60 days after the Department's Notice of Tentative Determination of Claim, file a protest thereto and request a hearing thereon, the Department shall give notice to such claimant, or the legal representative of a deceased claimant or claimant who is a person under legal disability, of the time and place fixed for such hearing, and shall hold a hearing in conformity with the provisions of this Act, and pursuant thereto shall issue its Final Determination of the amount, if any, found to be due as a result of such hearing, to such claimant, or the legal representative of a deceased or incompetent claimant.
If a protest to the Department's Notice of Tentative Determination of Claim is not filed within 60 days and a request for a hearing thereon is not made as provided herein, the Notice shall thereupon become and operate as a Final Determination; and, if the Department's Notice of Tentative Determination upon becoming a Final Determination, indicates no amount due to the claimant, or, upon issuance of a credit or refund for the amount, if any, found by the Department to be due, the claim in all its aspects shall be closed and no longer open to protest, hearing, judicial review, or by any other proceeding or action whatever, either before the Department or in any court of this State. Claims for credit or refund hereunder must be filed with and initially determined by the Department, the remedy herein provided being exclusive; and no court shall have jurisdiction to determine the merits of any claim except upon review as provided in this Act.
35 ILCS 110/18