10 ILCS 5/6-2
The electors of any city now existing in this state may adopt and become entitled to the benefits of this Article 6 and Articles 14 and 18 of this Act in the manner following:
Whenever one thousand of the legal voters of such city voting at the last preceding election shall petition the circuit court of the county in which such city is located, to submit to a vote of the electors of such city the proposition as to whether such city and the electors thereof shall adopt and become entitled to the benefits of this Article, and said Articles 14 and 18 of this Act, it shall be the duty of such circuit court to order such proposition to be submitted accordingly at the next succeeding general or regularly scheduled municipal election; and if such proposition is not adopted at such election, the same shall in like manner be submitted to a vote of the electors of such city by said circuit court upon a like application at any general or regularly scheduled municipal election thereafter. If one thousand shall exceed one-eighth of the legal voters of any such city voting at the last preceding general or consolidated election, then such application need not be signed or made by more than one-eighth of the legal voters of such city voting at the last preceding general or consolidated election. Such petition shall be subject to the applicable provisions of Article 28 of this Code.
10 ILCS 5/6-2