35 ILCS 200/18-270

County clerks shall deliver the books for the collection of taxes and the books for the collection of taxes charged against railroad property to the duly qualified county or township collectors on or before December 31 annually, or as soon as practicable. Each collector shall receive the books or as soon as he or she is qualified. However, for the 10 years next following the completion of a general reassessment of property in any county with 3,000,000 or more inhabitants made under an order of the Department, as soon as such books are ready for delivery the county clerk shall specify a day for the delivery of the books to the collectors, shall give notice to the collectors of the specified day, and shall deliver the books on that day.