65 ILCS 5/2-2-14
In any county of between 150,000 and 1,000,000 population which has adopted an official plan under "An Act to provide for regional planning and for the creation, organization and powers of regional planning commissions", approved June 25, 1929, as amended, the county board, by resolution, may provide that before the question of incorporating a city under this Division is submitted to the electors in response to a petition filed under Section 2-2-6 the county board must first determine that (1) the proposed incorporation is compatible with the official plan for the development of the county, and (2) the lands described in the petition as intended to be embraced in the proposed city constitute a sufficient tax base as will insure the ability of the city to provide all necessary municipal services to its inhabitants. When such a resolution is in effect, the court in which such a petition is filed shall first require a showing that those determinations have been made by the county board. If no such showing is made the court shall deny the petition. If such a showing is made, the court shall proceed as provided in Section 2-2-6.
65 ILCS 5/2-2-14