765 ILCS 205/2
The plat must be completed, a statement from a Registered Land Surveyor attached and acknowledged by the owner of the land, or his attorney duly authorized, in the same manner as deeds of land are required to be acknowledged. The plat must be submitted to the city council of the city or board of trustees of the village or town or to the officer designated by them, for their or his approval, if the land subdivided is located within the corporate limits of any such city, village or town or within contiguous territory which is affected by an official plan, or part thereof, of any city, village or town. If the land subdivided is located outside the corporate limits of any city, village or town and is not affected by such official plan, or part thereof, the plat must be submitted to the county board of the county in which the land is located for its approval. Within 3 business days after a plat is submitted for approval, the city council, board of trustees, designated officer, or county board shall notify the president of the school board of each school district in which any of the subdivided land is located that the plat has been submitted for approval and that it is available for inspection. The notice shall also give the date, time, and place of the hearing on approval or disapproval of the plat. The notice shall be served by certified mail, return receipt requested, or by personal delivery. Failure to notify the school board as required by this Section does not invalidate the plat.
Neither the city council of the city, the board of trustees of the village or town or the officer designated by them, or the county board of the county shall approve such plat, unless, in addition to any other requirements of such council, board of trustees or county board or the officer or officers designated by them, the topographical and profile studies to be submitted with the subdivision plat have on their face the signed statement of a Registered Professional Engineer, and the owner of the land or his duly authorized attorney, to the effect that to the best of their knowledge and belief the drainage of surface waters will not be changed by the construction of such subdivision or any part thereof, or, that if such surface water drainage will be changed, reasonable provision has been made for collection and diversion of such surface waters into public areas, or drains which the subdivider has a right to use, and that such surface waters will be planned for in accordance with generally accepted engineering practices so as to reduce the likelihood of damage to the adjoining property because of the construction of the subdivision. The topographical and profile studies required herein shall not be recorded, but shall be retained and filed by city, village or county to which submitted for approval of the subdivision plat, as permanent public documents.
Neither the city council of the city, the board of trustees of the village or town or the officer designated by them, or the county board of the county shall approve such plat, unless, in addition to any other requirements of such council, board of trustees or county board or the officer or officers designated by them, the plat has been approved in writing (i) except in municipalities with a population of 1,000,000 or more, by the Illinois Department of Transportation with respect to roadway access where such access is to a state highway, (ii) by the relevant local highway authority with respect to all other roadway access, and (iii) by the local health department, if one exists, with respect to sewage disposal systems if any part of the platted land will not be served by a public sewer system. An applicant shall simultaneously file with the Illinois Department of Transportation, relevant local highway authority, or local health department, as appropriate, a copy of the application for preliminary approval of a proposed plat that is filed with the municipality or county. The department or authority receiving the application shall review the application based solely upon safety or access control standards and provide written approval or disapproval to the municipal or county plan commission and to the municipal or county corporate authorities not later than 90 days from the date the application is received. The 90 day period may be changed by mutual agreement. If disapproved, the department or authority shall provide reasons for the disapproval related to safety or access control standards and identify improvements that will remove the disapproval. The municipal or county corporate authorities may approve the plat once the improvements have been incorporated into the application or in the event that the department or authority fails to respond in writing to the municipality or county within the 90 day period or other period established by mutual agreement. The failure of the city council of a municipality with a population of 1,000,000 or more to obtain approval of a plat in writing by the Illinois Department of Transportation with respect to roadway access where such access is to a State highway, prior to the approval of any such plat as required by this Section, where such failure occurred on or after January 1, 1988 and before the effective date of this amendatory Act of 1989, shall not affect the validity of such plat, and any such plat otherwise complying with the provisions of this Section is validated.
The statement of the Registered Land Surveyor and of acknowledgment, together with the plat, must be recorded by the Land Surveyor who prepared the plat, or a person designated by that Land Surveyor, or upon the death, incapacity, or absence of that Land Surveyor, by the owner of the land or his or her representative, in the recorder's office of the county in which the land is situated, or if the title to the land is registered under the Land Titles Act, must be filed in the office of the registrar of titles for the county, and such acknowledgment and recording or such acknowledgment and filing as aforesaid, shall have like effect and certified copies thereof and of such plat, or of any plat heretofore acknowledged and certified according to law, may be used in evidence to the same extent and with like effect, as in case of deeds. The recorder or registrar of titles shall not record or register a plat offered for recording or registration after October 1, 1977, unless such plat is at least 8 1/2 inches by 14 inches but not more than 30 inches by 36 inches. In counties of 1,000,000 or more population the recorder or the registrar of titles must not record or register the plat unless the persons submitting the plat for recording or registration simultaneously therewith deliver to the recorder or registrar of titles 6 true and exact copies thereof. In all counties, the recorder or registrar of titles shall not record or register a plat, unless the plat states the current mailing address of the person submitting the plat for recording or registration. Any changes to the unrecorded plat as may be desired or required by any party must be made by the Registered Land Surveyor who prepared the original plat, and in the event of the death, incapacity, or absence of that Land Surveyor, by another Registered Land Surveyor who shall specifically identify the change or changes made on the face of the plat.
An original plat, having been properly certified, acknowledged, approved and recorded or filed as above provided in this Section, may be retained as the permanent record by the recorder or registrar.
765 ILCS 205/2