Ill. Const. Transition Schedule, § 5

(a) The number of members of a county board in a county which, as of the effective date of this Constitution, elects three members at large may be changed only as approved by county-wide referendum. If the number of members of such a county board is changed by county-wide referendum, the provisions of Section 3(a) of Article VII relating to the number of members of a county board shall govern thereafter.

(b) In Cook County, until (1) a method of election of county board members different from the method in existence on the effective date of this Constitution is approved by a majority of votes cast both in Chicago and in the area outside Chicago in a county-wide referendum or (2) the Cook County Board by ordinance divides the county into single member districts from which members of the County Board resident in each district are elected, the number of members of the Cook County Board shall be fifteen except that the county board may increase the number if necessary to comply with apportionment requirements. If either of the foregoing changes is made, the provisions of Section 3(a) of Article VII shall apply thereafter to Cook County.

(c) Townships in existence on the effective date of this Constitution are continued until consolidated, merged, divided or dissolved in accordance with Section 5 of Article VII.