70 ILCS 2205/14.3
Any sanitary district may annex any territory which is not within the corporate limits of the sanitary district but which is contiguous to it and is served by the sanitary district or by a municipality with sanitary sewers that are connected and served by the sanitary district by the passage of an ordinance to that effect by the board of trustees, describing the territory to be annexed. A copy of the ordinance with an accurate map of the annexed territory, certified as correct by the clerk of the district shall be filed with the county clerk of the county in which the annexed territory is located. The new boundary shall extend to the far side of any adjacent highway and shall include all of every highway within the area annexed. These highways shall be considered to be annexed even though not included in the legal description set forth in the annexation ordinance.
70 ILCS 2205/14.3