70 ILCS 605/1-4
The circuit courts of the several counties have jurisdiction over all matters and proceedings pertaining to the organization and operation of drainage districts. In those instances in which all the land in a proposed district is situated in a single county, the petition for the organization of that district shall be filed with, and all subsequent proceedings shall be had in, the circuit court of that county. In those instances in which the land in a proposed district is situated in 2 or more counties, the proceedings for the organization and operation of the district shall be had in the circuit court of the county in which the greater portion of the land in the proposed district is situated. After a district has been organized under this Act all proceedings pertaining to the operation of that district shall be had in the court which organized the district without regard to changes in boundaries or area by annexation, detachment or otherwise.
A district heretofore organized by a circuit court shall be deemed to have been organized in the county in which the court so organizing the district was located. A district heretofore organized by any method other than by order of any court of record shall be deemed to have been organized in the county in which the greater portion of its land is situated at the time when this Act goes into effect, unless it is impossible to determine, without a survey, the county in which the greater portion of its land is situated and in that event the commissioners of the district shall have the power to determine the county in which the district shall be deemed to have been organized.
70 ILCS 605/1-4