How to appeal your Illinois property taxes

Who has to prove what

PTAB, 86 Ill. Adm. Code 1910.63(e): 'When market value is the basis of the appeal, the value of the subject property must be proved by a preponderance of the evidence. When unequal treatment in the assessment process is the basis of the appeal, the inequity of the assessments must be proved by clear and convincing evidence.' Circuit court, 35 ILCS 200/23-15(b)(2): 'The plaintiff has the burden of proving any contested matter of fact by clear and convincing evidence.' PTAB decisions are 'based upon equity and the weight of evidence and not upon constructive fraud' (35 ILCS 200/16-185); 23-15(b)(3) abolishes constructive fraud for court challenges.

primary source · verified 2026-08-12

When values are set

COOK COUNTY: triennial. 'Cook County follows a triennial reassessment cycle, meaning that a property is reassessed once every three years. A property's reassessment year depends on the township in which the property is located.' Three reassessment districts across 38 townships: City of Chicago, North Suburbs, and South & West Suburbs. CURRENT CYCLE: 'In 2026, the south and west suburbs of Cook County will undergo reassessment.' Rotation confirmed by archived Assessor calendars: 2023 South & West, 2024 City of Chicago, 2025 North Suburbs, 2026 South & West. 2026 South/West townships listed by the Assessor: Stickney, Lyons, Bremen, Lemont, Worth, Calumet, Proviso, Orland, Thornton, Rich, Bloom, River Forest, Riverside, Oak Park, Berwyn, Cicero, Palos. Because notices mail township-by-township, appeal windows open on a ROLLING basis and there is NO single Cook County appeal deadline. ALL OTHER ILLINOIS COUNTIES: quadrennial general assessment - Illinois Department of Revenue Pub-136: 'all other property must be viewed, inspected, and revalued every four years. The only exception is for Cook County, which has a three-year reassessment cycle.' ASSESSMENT LEVEL: 35 ILCS 200/9-145 - 'Except in counties with more than 200,000 inhabitants which classify property for purposes of taxation... Each tract or lot of property shall be valued at 33 1/3% of its fair cash value.' COOK CLASSIFICATION ORDINANCE (adopted by county board per 35 ILCS 200/9-150 and Ill. Const. art. IX sec. 4(b)): Class 1 vacant 10%, Class 2 residential 10%, Class 3 multi-family 10%, Class 4 not-for-profit 20%, Class 5A commercial 25%, Class 5B industrial 25%, incentive Classes 6/7/8/C/L/S at reduced levels. Cook County Assessor: 'For residential property, this is usually 10% of the estimated market value. For commercial property, this is typically 25%.' STATE MULTIPLIER: 35 ILCS 200/17-5 - the Department of Revenue 'shall lower or raise the total assessed value of property in each county... so that the property will be assessed at 33 1/3% of its fair cash value,' using a 3-year median ratio study; 17-30 requires certification of the final factor to each county clerk. Pub-136: 'a blanket percentage change (increase or decrease), called an equalization factor or multiplier, is applied to all non-farm property to bring the level of assessments to 33 1/3 percent.'

primary source · verified 2026-08-12

How counties differ

THE LADDER AND THE MUTUALLY EXCLUSIVE ELECTION. Assessor (informal, free, optional) -> County Board of Review -> then the taxpayer must ELECT one of two paths: (A) Property Tax Appeal Board, or (B) a circuit court tax objection complaint under 35 ILCS 200/23-5 et seq. The election is one-way: 35 ILCS 200/16-160 - 'If a petition is filed by a taxpayer, the taxpayer is precluded from filing objections based upon valuation, as may otherwise be permitted by Sections 21-175 and 23-5. However, any taxpayer not satisfied with the decision of the board of review... need not appeal the decision to the Property Tax Appeal Board before seeking relief in the courts.' So filing at PTAB forfeits the valuation-based court objection, but going to court does not require exhausting PTAB. The court route separately requires exhaustion of the Board of Review remedy - 35 ILCS 200/23-10: 'An objection to an assessment for any year shall not be allowed by the court... 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.' The court route also requires payment of all tax due within 60 days of the first penalty date (23-5), which is deemed paid under protest. Also jurisdictional: 16-160 - 'If an appeal is dismissed for failure to appear at a board of review or board of appeals hearing, the Property Tax Appeal Board shall have no jurisdiction to hear any subsequent appeal on that taxpayer's complaint.' COOK vs COLLAR COUNTIES. Cook: triennial, classification ordinance (residential 10%), rolling township deadlines at BOTH the Assessor and the Board of Review, attorney required at the Board of Review for entities but NOT at the Assessor, filing free at every level. DuPage: Board of Review deadline is 'thirty days after the publication of the township assessment roll' (Board Rule 8: 'All appeals must be e-filed no later than thirty days after legal publication of assessments of the relevant township'); mandatory e-file; both sales and assessment/uniformity comparables accepted - 'This evidence should include three (or more) comparable properties... If the appeal is based on assessment uniformity, the comparables should be similar properties with similar amenities'; Rule 9 says 'Usually three (but not more than five)'; Rule 10 mirrors the PTAB two-tier burden (preponderance for value, clear and convincing for inequity); appraisals accepted up to 10 calendar days after the filing deadline. 2025 DuPage examples: Downers Grove published 8/14/2025, filing closed 9/15/2025; Bloomingdale 8/29/2025 to 9/29/2025; Naperville 9/24/2025 to 10/24/2025; Milton and Addison 10/24/2025 to 11/24/2025. Lake: 'on or before thirty (30) days after the date of publication of current assessments for a particular township'; mandatory Smartfile e-filing; Lake County Comparable Property Grid; 'it is preferable to select at least three (3) comparable properties (Lake County comparison grid allows five)' for both value and equity, and 'it may take more than three (3) comparable properties to prove unequal treatment'; clear and convincing standard for inequity. Published 2026 Lake deadlines: Benton and Ela published 7/23/2026, close 8/24/2026; Warren and Waukegan 8/6/2026 to 9/8/2026; Grant, Wauconda, West Deerfield, Zion 8/13/2026 to 9/14/2026; Cuba and Libertyville 8/20/2026 to 9/21/2026. NO APPRAISAL-ABOVE-A-THRESHOLD RULE was found in DuPage or Lake - both regulate appraisal standards (USPAP, Illinois-licensed appraiser) and submission timing, not a dollar trigger. The only $100,000 thresholds in Illinois practice are procedural: 35 ILCS 200/16-55(i) requires serving all taxing districts where a change of $100,000 or more is sought; PTAB guidance notes residential appeals seeking under $100,000 in assessed-value change may use comparables or an appraisal, while 'For commercial and industrial appeals, an appraisal is recommended'; and Cook 14-15 administrative certification is limited to reductions under $100,000.