35 ILCS 640/2-13
Every delivering supplier maintaining a place of business in this State who is obligated to collect and remit the tax imposed on a purchaser by this Law, and every self-assessing purchaser who is obligated to pay the tax imposed by this Law directly to the Department, shall keep books, records, papers and other documents which are adequate to reflect the information which such supplier or such self-assessing purchaser, as the case may be, is required by Section 2-9 or Section 2-11 of this Law to report to the Department by filing returns with the Department. All books and records and other papers and documents required by this Law to be kept shall be kept in the English language and shall, at all times during business hours of the day, be subject to inspection by the Department or its duly authorized agents and employees. Books and records reflecting purchase price paid and kilowatt-hours delivered, used or consumed during any period with respect to which the Department is authorized to establish liability as provided in Section 2-12 of this Law shall be preserved until the expiration of such period unless the Department, in writing, authorizes their destruction or disposal at an earlier date.
The Department may, upon written authorization of the Director, destroy any returns or any records, papers or memoranda pertaining to such returns upon the expiration of any period covered by such returns with respect to which the Department is authorized to establish liability.
35 ILCS 640/2-13