10 ILCS 5/23-1.5a
Within 20 days of the filing of a Petition of State Election Contest, each candidate in the election contested may become a party to the contest proceeding by entering his or her written appearance or otherwise filing written pleadings in response to the Petition of State Election Contest with the Clerk of the Supreme Court. The responsive pleadings may include a motion to dismiss, challenging the sufficiency of the Petition of State Election contest or any part thereof. Any candidate who does not so enter his or her appearance shall not be entitled to further notice of the contest proceeding nor be permitted to take part in the proceeding on his or her own behalf. Failure to file an appearance, however, shall not affect a candidate's right to office if he or she is determined to have received the highest number of votes.
10 ILCS 5/23-1.5a