35 ILCS 120/6b
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 taxpayer's legal representative, in the event that the taxpayer has died or become incompetent, 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 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 or incompetent taxpayer, within 60 days after the Department's Notice of Tentative Determination of Claim, files a protest thereto and requests a hearing thereon, the Department shall give notice to such claimant, or the legal representative of a deceased taxpayer, or a taxpayer who is 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 taxpayer, or a taxpayer who is under legal disability. The Department's Final Determination may be reviewed by the proper Circuit Court, in the same manner, within the same time, upon the same terms and conditions and to the same extent, as provided by Section 12 of this Act.
In any case in which there has been an erroneous refund of tax payable under this Act, a notice of tax liability may be issued at any time within 3 years from the making of that refund, or within 5 years from the making of that refund if it appears that any part of the refund was induced by fraud or the misrepresentation of a material fact. The amount of any proposed assessment set forth in the notice shall be limited to the amount of the erroneous refund.
35 ILCS 120/6b