35 ILCS 200/23-10
Beginning with the 2003 tax year, in counties with 3,000,000 or more inhabitants, the person paying the taxes due as provided in Section 23-5 may file a tax objection complaint under Section 23-15 within 165 days after the first penalty date of the final installment of taxes for the year in question. Beginning with the 2003 tax year, in counties with less than 3,000,000 inhabitants, the person paying the taxes due as provided in Section 23-5 may file a tax objection complaint under Section 23-15 within 75 days after the first penalty date of the final installment of taxes for the year in question. However, in all counties in cases in which the complaint is permitted to be filed without payment under Section 23-5, it must be filed prior to the entry of judgment under Section 21-175. In addition, the time specified for payment of the tax provided in Section 23-5 shall not be construed to delay or prevent the entry of judgment against, or the sale of, tax delinquent property if the taxes have not been paid prior to the entry of judgment under Section 21-175. An objection to an assessment for any year shall not be allowed by the court, however, if an administrative remedy was available by complaint to the board of appeals or board of review under Section 16-55 or Section 16-115, unless that remedy was exhausted prior to the filing of the tax objection complaint.
When any complaint is filed with the court in a county with less than 3,000,000 inhabitants, the plaintiff shall file 3 copies of the complaint with the clerk of the circuit court. Any complaint or amendment thereto shall contain (i) on the first page a listing of the taxing districts against which the complaint is directed and (ii) a summary of the reasons for the tax objections set forth in the complaint with enough copies of the summary to be distributed to each of the taxing districts against which the complaint is directed. Within 10 days after the complaint is filed, the clerk of the circuit court shall deliver one copy to the State's Attorney and one copy to the county clerk, taking their receipts therefor. The county clerk shall, within 30 days from the last day for the filing of complaints, notify the duly elected or appointed custodian of funds for each taxing district that may be affected by the complaint, stating (i) that a complaint has been filed and (ii) the summary of the reasons for the tax objections set forth in the complaint. Any amendment to a complaint, except any amendment permitted to be made in open court during the course of a hearing on the complaint, shall also be filed in triplicate, with one copy delivered to the State's Attorney and one copy delivered to the county clerk by the clerk of the circuit court. The State's Attorney shall within 10 days of receiving his or her copy of the amendment notify the duly elected or appointed custodian of funds for each taxing district whose tax monies may be affected by the amendment, stating (i) that the amendment has been filed and (ii) the summary of the reasons for the tax objections set forth in the amended complaint. The State's Attorney shall also notify the custodian and the county clerk in writing of the date, time and place of any hearing before the court to be held upon the complaint or amended complaint not later than 4 days prior to the hearing. The notices provided in this Section shall be by letter addressed to the custodian or the county clerk and may be mailed by regular mail, postage prepaid, postmarked within the required period, but not less than 4 days before a hearing.
35 ILCS 200/23-10