30 ILCS 20/5

All records of receipts and disbursements by county treasurers and ex-officio county collectors, including paid or cancelled checks, warrants, orders, drafts or vouchers, and other evidences, shall be preserved and turned over to their successors in office: Provided, paid or cancelled checks, warrants, orders, drafts or vouchers, and other evidences, shall be arranged in the order of their dates, and under proper headings, and sealed. Such sealed packages shall be preserved in a public vault, or warehouse, and shall not be opened except in the presence or upon notice and an opportunity to be present to the officer, his agent or personal representative.