35 ILCS 200/6-45
If any county contains within its limits 3,000,000 or more inhabitants, as determined by the last Federal decennial or special census, that county shall at once come under the provisions of this Code relating to counties of that population, and at the next ensuing regular election of county officers, a county assessor shall be elected, and all provisions of this Code relating to counties with 3,000,000 or more inhabitants shall then immediately apply to that county.
In counties having an elected board of review as provided by law for counties with 150,000 or more but less than 3,000,000 inhabitants, the county board may by resolution have submitted to the legal voters of the county at any regular election, the question of abolishing the elected board of review. The county board shall certify the question to the proper election officials, who shall submit the question to the voters. Such referendum shall be held and returns made all in the manner now provided by the general election law and the question shall be in substantially the following form:
------------------------------------------------------------------------ Shall the elected board of YES review be abolished and be -------------------------------- replaced by an appointed board? NO ------------------------------------------------------------------------
If a majority of the voters voting on the question vote in favor of the proposition, the elected board of review shall be abolished to take effect on June 1 following the election. On that date, all records, books and papers pertaining to the elected board shall be transferred and delivered by the board to its successor in office. Thereafter all the powers and duties conferred upon appointed boards of review in counties with less than 3,000,000 inhabitants, shall be exercised and performed in such counties so voting, by appointed boards of review as provided by law for counties with less than 3,000,000 inhabitants.
35 ILCS 200/6-45