Illinois Statutes Chapter 10. Elections § 5/1-6. Computing dates of various acts; Saturday, Sunday, and holidays

(a) If the first or last day fixed by law to do any act required or allowed by this Code falls on a State holiday or a Saturday or a Sunday, the period shall extend through the first business day next following the day otherwise fixed as the first or last day, irrespective of whether any election authority or local election official conducts business on the State holiday, Saturday, or Sunday.

(b) For the purposes of this Section, “State holiday” means New Year's Day, Dr. Martin Luther King, Jr.'s Birthday, Lincoln's Birthday, President's Day, Casimir Pulaski's Birthday, Good Friday, 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.

(c) Notwithstanding any other provision of this Code, nominating papers, petitions of objection to nominating papers, certificates of withdrawal of candidacy, and reports of political committees actually received by election authorities and local election officials on a State holiday, a Saturday, or a Sunday shall not be deemed invalid or defective for that reason alone.