35 ILCS 200/18-215
For purposes of this Law, when 2 or more taxing districts merge or consolidate, the sum of the last preceding aggregate extensions for each taxing district shall be combined for the resulting merged or consolidated taxing district. When a service performed by one taxing district is transferred to another taxing district, that part of the aggregate extension base for that purpose shall be transferred and added to the aggregate extension base of the transferee taxing district for purposes of this Law and shall be deducted from the aggregate extension base of the transferor taxing district. If the service and corresponding portion of the aggregate extension base transferred to the taxing district are for a service that the transferee district does not currently levy for, the provisions of Section 18-190 of this Law requiring a referendum to establish a new levy shall not apply.
35 ILCS 200/18-215