35 ILCS 135/13a
In case any person who is required to file a return under this Act fails to file such return, the Department shall determine the amount of tax due from him according to its best judgment and information, which amount so fixed by the Department shall be prima facie correct and shall be prima facie evidence of the correctness of the amount of tax due, as shown in such determination. 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 amount of tax due, as shown therein. The Department shall issue such person a notice of tax liability for the amount of tax claimed by the Department to be due, together with a penalty in an amount determined in accordance with Sections 3-3, 3-5 and 3-6 of the Uniform Penalty and Interest Act. Except as otherwise provided in this Section, if such person or the legal representative of such person, within 60 days after such notice, files a protest to such notice of tax liability and requests a hearing thereon, the Department shall give notice to such person or the legal representative of such person 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 a final assessment to such person or to the legal representative of such person for the amount found to be due as a result of such hearing. Effective July 1, 2013, protests concerning matters that are subject to the jurisdiction of the Illinois Independent Tax Tribunal shall be filed with the Tribunal in accordance with the Illinois Independent Tax Tribunal Act of 2012, and hearings concerning those matters shall be held before the Tribunal in accordance with that Act. With respect to protests filed with the Department prior to July 1, 2013 that would otherwise be subject to the jurisdiction of the Illinois Independent Tax Tribunal, the person filing the protest may elect to be subject to the provisions of the Illinois Independent Tax Tribunal Act of 2012 at any time on or after July 1, 2013, but not later than 30 days after the date on which the protest was filed. If made, the election shall be irrevocable. If a protest to the notice of tax liability and a request for a hearing thereon is not filed within the time allowed by law , such notice of tax liability shall become final without the necessity of a final assessment being issued and shall be deemed to be a final assessment.
35 ILCS 135/13a