65 ILCS 5/7-1-1
Any territory that is not within the corporate limits of any municipality but is contiguous to a municipality may be annexed to the municipality as provided in this Article. For the purposes of this Article any territory to be annexed to a municipality shall be considered to be contiguous to the municipality notwithstanding that the territory is separated from the municipality by a lake, river, or other waterway or the territory is separated from the municipality by a strip parcel, railroad or public utility right-of-way, or former railroad right-of-way that has been converted to a recreational trail, but upon annexation the area included within that strip parcel, right-of-way, or former right-of-way shall not be considered to be annexed to the municipality. For purposes of this Section, "strip parcel" means a separation no wider than 30 feet between the territory to be annexed and the municipal boundary.
Except in counties with a population of more than 600,000 but less than 3,000,000, territory which is not contiguous to a municipality but is separated therefrom only by a forest preserve district, federal wildlife refuge, open land or open space that is part of an open space program, as defined in Section 115-5 of the Township Code, or conservation area, may be annexed to the municipality pursuant to Section 7-1-7 or 7-1-8, but only if the annexing municipality can show that the forest preserve district, federal wildlife refuge, open land, open space, or conservation area creates an artificial barrier preventing the annexation and that the location of the forest preserve district, federal wildlife refuge, open land, open space, or conservation area property prevents the orderly natural growth of the annexing municipality. Except for parcels of land less than one acre in size, it shall be conclusively presumed that the forest preserve district, federal wildlife refuge, open land, open space, or conservation area does not create an artificial barrier if the property sought to be annexed is bounded on at least 3 sides by (i) one or more other municipalities (other than the municipality seeking annexation through the existing forest preserve district, federal wildlife refuge, open land, open space, or conservation area), (ii) forest preserve district property, federal wildlife refuge, open land, open space, or conservation area, or (iii) a combination of other municipalities and forest preserve district property, federal wildlife refuge property, open land, open space, or conservation area. Except of parcels of land less than one acre in size, it shall also be conclusively presumed that the forest preserve district, federal wildlife refuge, open land, open space, or conservation area does not create an artificial barrier if the municipality seeking annexation is not the closest municipality within the county to the property to be annexed. The territory included within such forest preserve district, federal wildlife refuge, open land, open space, or conservation area shall not be annexed to the municipality nor shall the territory of the forest preserve district, federal wildlife refuge, open land, open space, or conservation area be subject to rights-of-way for access or services between the parts of the municipality separated by the forest preserve district, federal wildlife refuge, open land, open space, or conservation area without the consent of the governing body of the forest preserve district or federal wildlife refuge. Parcels of land less than one acre in size may be annexed to the municipality pursuant to Section 7-1-7 or 7-1-8 if it would be contiguous to the municipality but for the separation therefrom by a forest preserve district, federal wildlife refuge, open land or open space that is part of an open space program, as defined in Section 115-5 of the Township Code, or conservation area. The changes made to this Section by Public Act 91-824 are declaratory of existing law and shall not be construed as a new enactment.
For the purpose of this Section, "conservation area" means an area dedicated to conservation and owned by a not-for-profit organized under Section 501(c)(3) of the Internal Revenue Code of 1986, or any area owned by a conservation district.
In counties that are contiguous to the Mississippi River with populations of more than 200,000 but less than 255,000, a municipality that is partially located in territory that is wholly surrounded by the Mississippi River and a canal, connected at both ends to the Mississippi River and located on property owned by the United States of America, may annex noncontiguous territory in the surrounded territory under Sections 7-1-7, 7-1-8, or 7-1-9 if that territory is separated from the municipality by property owned by the United States of America, but that federal property shall not be annexed without the consent of the federal government.
For the purposes of this Article, any territory to be annexed to a municipality that is located in a county with more than 500,000 inhabitants shall be considered to be contiguous to the municipality if only a river and a national heritage corridor separate the territory from the municipality. Upon annexation, no river or national heritage corridor shall be considered annexed to the municipality.
When any land proposed to be annexed is part of any Fire Protection District or of any Public Library District and the annexing municipality provides fire protection or a public library, as the case may be, the Trustees of each District shall be notified in writing by certified or registered mail before any court hearing or other action is taken for annexation. The notice shall be served 10 days in advance. An affidavit that service of notice has been had as provided by this Section must be filed with the clerk of the court in which the annexation proceedings are pending or will be instituted or, when no court proceedings are involved, with the recorder for the county where the land is situated. No annexation of that land is effective unless service is had and the affidavit filed as provided in this Section.
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 petition for annexation. When any land proposed to be annexed includes any highway under the jurisdiction of any township, the Township Commissioner of Highways, the Board of Town Trustees, the Township Supervisor, and the Township Clerk shall be notified in writing by certified or registered mail before any court hearing or other action is taken for annexation. In the event that a municipality fails to notify the Township Commissioner of Highways, the Board of Town Trustees, the Township Supervisor, and the Township Clerk of the annexation of an area within the township, the municipality shall reimburse that township for any loss or liability caused by the failure to give notice. If any municipality has annexed any area before October 1, 1975, and the legal description in the petition for annexation did not include the entire adjacent highway, any such annexation shall be valid and any highway adjacent to the area annexed shall be considered to be annexed notwithstanding the failure of the petition to annex to include the description of the entire adjacent highway.
When annexing territory separated from the municipality by a lake, river, or other waterway, the municipality also annexes the portion of the lake, river, or other waterway that would make the municipality and territory contiguous if the lake, river, or other waterway is under the jurisdiction and control of another unit of local government or the State, or the federal government if allowed under federal law, except for any territory within the corporate limits of another municipality.
Any annexation, disconnection and annexation, or disconnection under this Article of any territory must be reported by certified or registered mail by the corporate authority initiating the action to the election authorities having jurisdiction in the territory, the Department of Transportation, and the post office branches serving the territory within 30 days of the annexation, disconnection and annexation, or disconnection.
Failure to give notice to the required election authorities or post office branches will not invalidate the annexation or disconnection. For purposes of this Section "election authorities" means the county clerk where the clerk acts as the clerk of elections or the clerk of the election commission having jurisdiction.
No annexation, disconnection and annexation, or disconnection under this Article of territory having electors residing therein made (1) before any primary election to be held within the municipality affected thereby and after the time for filing petitions as a candidate for nomination to any office to be chosen at the primary election or (2) within 60 days before any general election to be held within the municipality shall be effective until the day after the date of the primary or general election, as the case may be.
For the purpose of this Section, a toll highway or connection between parcels via an overpass bridge over a toll highway shall not be considered a deterrent to the definition of contiguous territory.
When territory is proposed to be annexed by court order under this Article, the corporate authorities or petitioners initiating the action shall notify each person who pays real estate taxes on property within that territory unless the person is a petitioner. The notice shall be served by certified or registered mail, return receipt requested, at least 20 days before a court hearing or other court action. If the person who pays real estate taxes on the property is not the owner of record, then the payor shall notify the owner of record of the proposed annexation.
65 ILCS 5/7-1-1