65 ILCS 5/7-2-8
The terms of all popularly elected officers in the boroughs shall expire 30 days after the first election of officers as provided in Sections 7-2-6 and 7-2-7. Until the expiration of their terms of office as provided herein, all elected officers in the boroughs shall continue to exercise all duties imposed by law, and shall take whatever steps are necessary and consistent with the provisions of this Division to effectuate the union of the municipalities. The terms of all popularly elected officers of the united city at the first election shall begin at the end of 30 days after the first election. The terms of the popularly elected officers of the united city shall end 30 days after the regular election at which their successors are chosen but if the successor to any such officer fails to qualify prior to the expiration of the 30-day period, the officer whose term thus expires shall continue to hold office and perform the duties of his office until such time as a successor qualifies for office. All appointed officers of each borough shall retain their offices and perform their duties in the borough for which they were appointed, until superseded by successors appointed for the united city. However, these appointed officers who are not superseded shall obey the orders of the officers of the united city.
65 ILCS 5/7-2-8