Mayor of Chicago

The mayoral term in Chicago was one year from 1837 through 1863, when it was increased to two years. In 1907 it was again lengthened to four years, the present duration. 
Until 1861, municipal elections were held in March. In that year, legislation changed them to April. In 1869, however, election time was changed to November, and terms expiring in April of that year were lengthened. 
In 1875, the election day was moved back to April by the city's vote to operate under the Cities and Villages Act of 1872. Lester L. Bond was the acting mayor when Joseph Medill left to a tour around Europe. Thomas Hoyne won election as mayor, but could not become the mayor so the election became a void. As of 1995, no mayor can run for a political party, they are considered as nonpartisans.
Vice Mayor.
The city council elects a vice mayor who is interim mayor in the event of a vacancy in the office of the mayor or the inability of the mayor to serve due to illness or injury. As of May 2019, the current vice mayor is Tom Tunney.
Past holders of this office have included Brendan Reilly (2015–2019) Ray Suarez (2011–2015), and David Orr.
Notes.
1 Rahm Emanuel is a Democrat, but he and all other candidates in the 2011 election officially ran as nonpartisans. Under a 1995 Illinois law, "candidates for mayor . . . no longer would run under party labels in Chicago."