35 ILCS 200/2-15
Any 2 or more contiguous townships in any one county, other than townships provided for in Sections 2-5 and 2-10, may by majority vote of each board of trustees of the townships, form a multi-township assessment district comprising those townships. This determination shall be made no later than October 1 of the year preceding the year in which township officials are elected. If one or more of those township assessor's offices is vacant, a determination to form a multi-township assessment district may still be made at the time of that vacancy. The assessor or assessors remaining in office in one or more of the townships comprising the multi-township assessment district shall assume the duties of multi-township assessor until a successor is elected or appointed and qualified. If there is no township assessor remaining in office at the time, the board of trustees of the multi-township assessment district, as defined in Section 2-20, shall appoint a multi-township assessor for the unexpired terms of the former elected township assessors as provided in this Code.
The township boards of trustees shall notify the supervisor of assessments and the Department prior to December 1 of the year in which they have taken any action prescribed in this Section.
35 ILCS 200/2-15