65 ILCS 5/11-15.1-3
Any such agreement executed after July 31, 1963 and all amendments of annexation agreements, shall be entered into in the following manner. The corporate authorities shall fix a time for and hold a public hearing upon the proposed annexation agreement or amendment, and shall give notice of the proposed agreement or amendment not more than 30 nor less than 15 days before the date fixed for the hearing. This notice shall be published at least once in one or more newspapers published in the municipality, or, if no newspaper is published therein, then in one or more newspapers with a general circulation within the annexing municipality. After such hearing the agreement or amendment may be modified before execution thereof. The annexation agreement or amendment shall be executed by the mayor or president and attested by the clerk of the municipality only after such hearing and upon the adoption of a resolution or ordinance directing such execution, which resolution or ordinance must be passed by a vote of two-thirds of the corporate authorities then holding office.
65 ILCS 5/11-15.1-3