Mayor Daniel Biss’s resignation is effective at 11:59 p.m. on October 18, 2026. Under state law, because more than 28 months remained in his term and the seat opened before candidate filing began, voters fill it at the April 6, 2027 election. [1][2]
Why only about two years
Biss was re-elected in April 2025 to a four-year term. The person elected in 2027 serves the rest of that term, through May 2029. [1]
The law behind it
Illinois law fills a vacancy in a four-year city office at the next city election when at least 28 months of the term remain and the vacancy happens before the petition-filing period opens. [2] A 2025 change to the law (P.A. 104-434) moved the trigger from “130 days before the election” to “before the period to file petitions,” which made October 19, 2026 the cutoff. [2][3]
The City Clerk says both conditions are met: the vacancy begins October 18, the day before filing opens on October 19. [1]