65 ILCS 5/7-1-29
If, as provided in Sections 7-1-16, 7-1-17, 7-1-27 and 7-1-28, petitions are presented to the court for the annexation of the whole and also for the annexation of a part or parts of a municipality to another municipality, the court shall order submitted to the electors the question specified in each petition. If the result of the voting at the election is against annexation of the whole, but favors annexation of a part, which is contiguous to the annexing municipality, this part is annexed to the annexing municipality, despite the unfavorable vote as to the annexation of the whole municipality. The same shall be true if the vote favors annexation of 2 or more parts, if the parts form a contiguous territory which is also contiguous to the annexing municipality.
65 ILCS 5/7-1-29