65 ILCS 5/7-1-27
Territory, within a municipality, which (1) is not less than one-half square mile in area, but less than the whole of the municipality, and which (2) is contiguous to another municipality, may be annexed to the latter municipality as follows:
A petition, signed by not less than 100 of the electors of the territory, shall be presented to the circuit court for the county wherein the annexing municipality is situated. The petition shall describe the territory and request that the question of the annexation of the territory be submitted to the electors of the territory and also to the electors of the disconnecting and annexing municipalities. If the petition is in conformity with the law, the court shall order the question of annexation of the territory submitted to the specified electors at a general municipal election to be held in each of the municipalities affected. The clerk of the circuit court shall certify the question for submission. No election for the annexation of any part of a municipality to another municipality shall be held within 22 months after a proposition to annex the whole or any part of a municipality to another municipality has been voted upon at any election.
65 ILCS 5/7-1-27