10 ILCS 5/23-1.2a
The results of an election, including a primary, for an elected executive officer provided for in Article V of the Constitution may be challenged (1) by any candidate whose name was on the ballot for that office, (2) by any person who filed a declaration of intent to be a write-in candidate for that office, or (3) by any person who voted in that election, provided that such person's challenge is supported by a verified petition signed by persons who voted in the election in a number no less than the largest number of signatures required to nominate a person to be a candidate of any political party which nominated a candidate for the office being contested.
Any person, including a candidate, qualified pursuant to this Section and desiring to contest the results of an election for such an office shall, within 15 days of the date of the official proclamation of results of such election, file a Petition of State Election Contest with the clerk of the Supreme Court together with a filing fee in the amount of $10,000.
10 ILCS 5/23-1.2a