65 ILCS 5/7-1-9

Whenever any contiguous, uninhabited, unincorporated territory is owned by any municipality, that territory may be annexed by that municipality by the passage of an ordinance to that effect, describing the territory to be annexed. A copy of the ordinance, with an accurate map of the annexed territory shall be recorded with the recorder of the county wherein the annexed territory is located and a document of annexation shall be filed with the county clerk and County Election Authority.