65 ILCS 5/7-1-25
Any unoccupied territory, lying along the boundary line between 2 adjoining municipalities, may be excluded from one of the adjoining municipalities and annexed to the other adjoining municipality, as follows:
The corporate authorities of the excluding municipality shall adopt an ordinance providing for such exclusion, and the corporate authorities of the annexing municipality shall adopt an ordinance providing for the annexation of this territory. Upon the adoption of these ordinances, the territory is thereby excluded from the one municipality and annexed to the other. The chief executive officer of each municipality thereupon shall file for recordation an accurate map of the excluded or added territory, as the case may be, together with a certified copy of the ordinance for exclusion or annexation with the recorder of the county in which the excluded or added territory, as the case may be, is situated.
65 ILCS 5/7-1-25