65 ILCS 20/21-12
At the time of election of the mayor there shall be elected also in a nonpartisan election a city clerk and a city treasurer. The candidates receiving a majority of the votes cast for clerk and treasurer at the consolidated primary election shall be declared the clerk and treasurer. If no candidate receives a majority of the votes for one of the offices, a runoff election shall be held at the consolidated election, when only the names of the candidates receiving the highest and second highest number of votes for that office at the consolidated primary election shall appear on the ballot. If more than one candidate received the highest or second highest number of votes for one of the offices at the consolidated primary election, the names of all candidates receiving the highest and second highest number of votes for that office shall appear on the ballot at the consolidated election. The candidate receiving the highest number of votes at the consolidated election shall be declared elected.
The clerk and treasurer each shall hold office for a term of 4 years beginning at noon on the third Monday in May following the election and until a successor is elected and qualified. No person, however, shall be elected to the office of city treasurer for 2 terms in succession unless the city, by ordinance, establishes different succession terms.
65 ILCS 20/21-12