65 ILCS 5/2-3-19
Each boundary of the municipality shall extend to the far side of any adjacent highway not included in any other municipality and shall include all of every highway within the area incorporated. These highways shall be considered to be incorporated even though not included in the legal description set forth in the petition for incorporation. When any land proposed to be incorporated includes any highway under the jurisdiction of any township, the township commissioner of highways and the board of town trustees shall be notified in writing by certified or registered mail before any court hearing or other action is taken for incorporation. If any municipality has been incorporated before January 1, 1986 and the legal description in the petition for incorporation did not include an adjacent highway, any such incorporation shall be valid and every highway adjacent to the area incorporated and not included in any other municipality shall be considered to be incorporated, notwithstanding the failure of the petition to incorporate to include the description of the adjacent highway.
65 ILCS 5/2-3-19