65 ILCS 5/7-1-24
On petition in writing, signed by one-half of the electors and one-half of the owners of record of land in any territory, not exceeding in area 160 acres, situated within any municipality, which territory is contiguous to another municipality, the corporate authorities of the municipality within which the territory is situated, may consent, by ordinance, that this territory be disconnected from such municipality and annexed to the other municipality to which the territory is contiguous. The ordinance must be passed by a majority vote of the corporate authorities of the disconnecting municipality. Thereupon the corporate authorities of the annexing municipality, by ordinance passed by a majority vote, may annex the territory. The territory, however, shall not be disconnected from the municipality of which it is a part until it is annexed to the municipality to which it is contiguous.
The clerk of the annexing municipality, within 90 days after the passage of the annexing ordinance, shall file for recordation a certified copy of the ordinance, with an accurate map of the territory annexed, with the recorder of the county in which the annexed territory is situated.
65 ILCS 5/7-1-24