765 ILCS 205/1.02

When any city, village, municipal corporation or political subdivision in the State annexes or disconnects territory, a plat of the land included in the disconnection or annexation must be filed with the recorder in the county or counties where the territory is located. In counties where the county clerk is not also the county recorder, a copy of the plat shall also be filed with the county clerk. Each plat shall state a legal description or descriptions sufficient to identify the boundaries of the annexed or disconnected territory, by reference to government surveys or by metes and bounds, including the section, township and range in which the territory is located. Such a plat must be prepared by a Registered Land Surveyor or in the case of cities, villages and incorporated towns by a Registered Land Surveyor or a duly employed municipal engineer registered under the laws of the State of Illinois, provided such engineer has had training in the field of civil engineering.