35 ILCS 605/18
In consideration of the grants, privileges and franchises herein conferred upon said company for the purposes aforesaid, the said company shall, on the first Mondays of December and June in each year, pay to the Department of Revenue of the State of Illinois five per centum on the gross or total proceeds, receipts or income derived from said road and branches, for the six months then next preceding. The first payment of such percentage on the main trunk of said road to commence four years from the date of said deed of trust, and on the branches, six years from the date aforesaid, unless said road and branches are sooner completed, then from the date of completion. And for the purpose of ascertaining the proceeds, receipts or income aforesaid, an accurate account shall be kept by said company, a copy whereof shall be furnished to the Governor of the State of Illinois and to the Department of Revenue; the truth of which account shall be verified by the affidavits of the treasurer and secretary of such company. And for the purpose of verifying and ascertaining the accuracy of such account, full power is hereby vested in the Governor of the State of Illinois, the Director of the Department of Revenue, or any other person by law appointed, to examine the books and papers of said corporation, and to examine, under oath, the officers, agents and employees of said company, and other persons. And if any person, so examined by the Governor or other authority, shall knowingly and wilfully swear falsely, or if the other officers making such affidavits shall knowingly and wilfully swear falsely, every such person shall be subject to the pains and penalties of perjury.
35 ILCS 605/18