55 ILCS 5/1-4015
If both the petitioning and adjoining counties are under township organization, the town officers shall not be in any manner affected by the union and annexation aforesaid. If the petitioning county is under township organization, and the adjoining county is not under township organization, the town officers shall continue to act as such until their respective terms of office shall expire; and the members of the county board of the petitioning county shall all sit with, and as a part of the county board of the adjoining county, as hereinbefore provided; and after the term of office of said town officers and said county board of the petitioning county shall expire the said township organization shall cease to exist. If the adjoining county is under township organization, and the petitioning county is not under township organization, immediately after the proclamation of the Governor aforesaid, the territory that had constituted the petitioning county shall be divided into towns, in the manner provided in the Township Code.
55 ILCS 5/1-4015