5 ILCS 490/60
The twelfth day of February of each year shall be a legal holiday to be known as Lincoln's Birthday to be observed as a day on which to hold appropriate exercises in commemoration of our illustrious President. When February twelfth shall fall on a Sunday, the following Monday shall be held and considered the holiday.
(from Ch. 1, par. 3051-60)
(Source: P.A. 87-272.)