10 ILCS 5/2A-54
In those cases in which the election to an office is changed by the consolidation of elections to an earlier or later month in the same year or to a different year, the term of any incumbent serving on December 1, 1980 is extended to the first Monday in the first month following the election of his successor and until the successor has qualified, and the term of the successor in office shall commence on that first Monday.
The term of office of a person elected at a nonpartisan election whose term begins before the effective date of this amendatory Act of 1997 shall expire on the date that his or her term would have expired had this amendatory Act of 1997 not been enacted. The term of office of a person elected at a consolidated election held on or after the effective date of this amendatory Act of 1997 to succeed to a term of office of a person elected at a nonpartisan election shall begin upon the termination of the predecessor's term of office. The term of office of a person elected to succeed to a term of office of a person elected at a nonpartisan election shall end after the next consolidated election at which a successor is elected and at the regularly scheduled time for the ending of terms of office as provided in the Act or Acts creating or governing that unit of local government or school district.
However, this general provision for the transition of terms of office in relation to the adoption of a uniform schedule of elections shall be subject to the specific provisions for the transition of terms of office in the several Acts creating or governing the creation of various units of local government and school districts, as amended.
10 ILCS 5/2A-54