65 ILCS 5/7-1-46
Neither the People of the State of Illinois nor any person, firm or corporation, public or private, nor any association of persons shall commence an action contesting either directly or indirectly the annexation of any territory to a municipality unless initiated within one year after the date such annexation becomes final or within one year of the effective date of this amendatory Act of 1965 whichever date occurs latest. This amendatory Act of 1965 shall apply to annexations made prior to the effective date of the Act as well as those made on or after the effective date. Where a limitation of a shorter period is prescribed by statute such shorter limitation applies. The limitation set forth in this section shall apply to any annexation, even where the judge, body or officer annexing the territory did not at the time of such annexation have jurisdiction of the subject matter, and irrespective of whether such annexation may otherwise be defective or void, except that the limitation of this Section shall not apply to annexations of territory which was not contiguous at the time of annexation and is not contiguous at the time an action is brought to contest such annexation.
65 ILCS 5/7-1-46