30 ILCS 500/15-45
The time within which any act provided in this Code is to be done shall be computed by excluding the first day and including the last, unless the last day is Saturday or Sunday or is a holiday, and then it shall also be excluded. If the day succeeding a Saturday, Sunday, or holiday is also a holiday, a Saturday, or a Sunday, then that succeeding day shall also be excluded. For the purposes of this Code, "holiday" means: New Year's Day; Dr. Martin Luther King, Jr.'s Birthday; Lincoln's Birthday; President's Day; Memorial Day; Juneteenth National Freedom Day; Independence Day; Labor Day; Columbus Day; Veterans' Day; Thanksgiving Day; Christmas Day; and any other day from time to time declared by the President of the United States or the Governor of Illinois to be a day during which the agencies of the State of Illinois that are ordinarily open to do business with the public shall be closed for business.
Notwithstanding any other provision of State law to the contrary, November 3, 2020 shall be a State holiday known as 2020 General Election Day and shall be observed throughout the State pursuant to this amendatory Act of the 101st General Assembly.
30 ILCS 500/15-45