On March 16, the Illinois Supreme Court unanimously ruled that candidate petitions are not valid unless they have the statutorily required number of valid signatures. Jackson-Hicks v The East St. Louis Board of Election Commissioners, 2015 IL 118929. This may seem to be obvious, but the lower state court had ruled last month that if a petition has almost enough valid signatures, it is in substantial compliance with the law.
As a result of the decision, the incumbent Mayor, Alvin L. Parks, Jr., will be removed from the ballot. The election is April 7 and some absentee votes have already been cast. Fortunately for Parks, the Illinois deadline for filing as a write-in candidate is only one week before the election, so he still has time to file as a declared write-in candidate. However, if the ballots (which have already been printed) are not reprinted, anyone who votes for him by placing an “X” in the square next to his name (as printed on the ballot) will have cast an invalid ballot. See this story. Thanks to Ken Bush for the link.
UPDATE: this March 18 story says all the ballots will be reprinted, and Mayor Parks will run as a write-in candidate.