Elective offices become vacant within the meaning of the Act, unless the context indicates otherwise, on the happening of any of the following events, before the expiration of the term of such office:
No elective office except as herein otherwise provided becomes vacant until the successor of the incumbent of such office has been appointed or elected, as the case may be, and qualified. The successor shall have the same type of residential qualifications as his or her predecessor and, if the residential requirements contained in Section 10-10.5, 11E-35, or 12-2 of this Code apply, the successor, whether elected or appointed by the remaining members or a regional superintendent, shall be an inhabitant of the particular area from which his or her predecessor was elected.
105 ILCS 5/10-11