65 ILCS 20/21-5.1
Following election and qualification of alderpersons at a general election as provided by Section 21-22 of this Act, the City Council shall elect, from among its members, a Vice Mayor, to serve as interim Mayor of Chicago in the event that a vacancy occurs in the office of Mayor or in the event that the Council determines, by 3/5 vote, that the Mayor is under a permanent or protracted disability caused by illness or injury which renders the Mayor unable to serve. The Vice Mayor shall serve as interim Mayor. He will serve until the City Council shall elect one of its members acting Mayor or until the mayoral term expires.
The Vice Mayor shall receive no compensation as such, but shall receive compensation as an alderperson even while serving as interim Mayor. While serving as interim Mayor, the Vice Mayor shall possess all rights and powers and shall perform the duties of Mayor.
65 ILCS 20/21-5.1