70 ILCS 2405/23.4
Any territory which is not within the corporate limits of any sanitary district but which is contiguous to a sanitary district and which territory has no electors residing therein; or any such territory with electors residing thereon; may be annexed to the sanitary district in the following manner: a written petition signed by the owners of record of all land within such territory, or if such territory is occupied, by the owners of record and by all electors residing thereon, shall be filed with the clerk of the sanitary district, which petition shall request annexation and shall state that no electors reside thereon (or that all such electors residing thereon join in the petition, whichever shall be the case) and shall be under oath. The board of trustees of the sanitary district to which annexation is sought shall then consider the question of the annexation of the described territory. A two-thirds vote of the board of trustees is required to annex. A copy of the ordinance annexing the territory together 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.
70 ILCS 2405/23.4