820 ILCS 310/19.1

The time within which any act is required to be performed under the provisions of this Act shall be computed by excluding the first day and including the last, unless the last day is Sunday or is a holiday as defined or fixed in any statute now or hereafter in force in this State, and then such days shall also be excluded. If the day succeeding such holiday is also a holiday then such succeeding day shall also be excluded.