Illinois Property Tax Appeals
Work out how far your assessment sits above comparable sales, what a reduction would save at your local rate, and what each of the three routes to it costs — filing yourself, a flat-fee service, or a contingency service. Every county deadline is cited to the authority that sets it.
Your data never leaves your device Learn more
Estimate only — not legal advice. This is the published math for Illinois assessment appeals, shown as a range. Your actual outcome depends on facts, evidence, and decisions this page cannot see.
When your protest is due in Illinois
Outside Cook County, 35 ILCS 200/16-55(d) sets the deadline at 30 calendar days after the assessment list is published under §12-10 — and publication dates differ by county and by township, so the operative date genuinely varies. §12-10 requires publication on or before December 31 and requires the published notice itself to state the deadline. In Cook County, §16-115 has complaints filed by township on the dates given in the §16-110 notices, which set only a floor of at least 20 days after publication. The state says so plainly: the Property Tax Appeal Board tells taxpayers to call the board of review or supervisor of assessments for the filing deadline each year, and in Cook to ask for the date for their township. A complaint sent by US mail is filed as of the postmark date (§16-55(d-5)). The second-stage deadline is firmer: 30 days after written notice of the board of review's decision (§16-160), or in Cook 30 days after that notice or after transmittal of final township action, whichever is later.
The rule
Set locally
Outside Cook County, 35 ILCS 200/16-55(d) sets the deadline at 30 calendar days after the assessment list is published under §12-10 — and publication dates differ by county and by township, so the operative date genuinely varies. §12-10 requires publication on or before December 31 and requires the published notice itself to state the deadline. In Cook County, §16-115 has complaints filed by township on the dates given in the §16-110 notices, which set only a floor of at least 20 days after publication. The state says so plainly: the Property Tax Appeal Board tells taxpayers to call the board of review or supervisor of assessments for the filing deadline each year, and in Cook to ask for the date for their township. A complaint sent by US mail is filed as of the postmark date (§16-55(d-5)). The second-stage deadline is firmer: 30 days after written notice of the board of review's decision (§16-160), or in Cook 30 days after that notice or after transmittal of final township action, whichever is later.
If the last day falls on a weekend or holiday: 5 ILCS 70/1.11: time is computed by excluding the first day and including the last, unless the last day is a Saturday, Sunday or statutory holiday, in which case it is excluded too — and if the following day is also a weekend or holiday, that day is excluded as well.5 ILCS 70/1.11
The date above is this state’s published rule applied to what you entered. Confirm it against the notice itself and the authority’s own instructions — most jurisdictions require their form or portal, and a letter alone may not open a protest.
How the appeal runs
First-level appeals are heard by the county board of review — in Cook County, the Board of Review under 35 ILCS 200/16-95. The state-level Property Tax Appeal Board is the second stage, not the first ↗.
- 01Obtain the property record card showing the assessed valuation.
- 02Discuss the assessment with the assessor to find out how it was calculated.
- 03Determine the fair market value of the property.
- 04Determine the prevailing assessment level in the district.
- 05Determine the basis for a formal complaint.
- 06File a written complaint on Form PTAX-230, Non-farm Assessment Complaint, with the county board of review.
- 07Present evidence of unfair assessment to the board of review. A written appeal to the board is a prerequisite to any further appeal to the Property Tax Appeal Board or to the circuit court.
Free to file: There is no charge for filing an appeal with the Property Tax Appeal Board, and neither the Property Tax Code nor the Department of Revenue publishes a fee for a county board of review complaint. A county may still publish its own.
Illinois assesses at 33.33% of market value, so an assessed figure is not directly comparable to a sale price — divide by the ratio first, as the assessment calculator does. 35 ILCS 200/9-145 values property at 33 1/3% of fair cash value, and §12-10 requires the published assessment notice to say so — but the section opens with an exception for counties over 200,000 inhabitants that classify property for taxation. Cook County classifies, so its residential percentage is set by county ordinance under §9-150 rather than by state law, and the 33 1/3% figure does not describe roughly forty per cent of the state's population. Cook's own percentages are county data and are not in this pack.
35 ILCS 200/16-55(d)
Work out whether you are over-assessed with the assessment calculator, then organise the evidence with the appeal letter generator.
Verified 2026-08-03 against 35 ILCS 200/16-55 (complaint to the board of review), 200/12-10 (publication of the assessment list), 200/16-110 and 200/16-115 (Cook County township deadlines), 200/16-160 (appeal to the Property Tax Appeal Board), 200/9-145 and 200/9-150 (valuation at 33 1/3% and the classification exception), with 5 ILCS 70/1.11 (Statute on Statutes) and the Illinois Department of Revenue's published appeal steps (effective 2026-01-01)
Source of record
- USA.gov — State and local taxes ↗Federal
- 35 ILCS 200/16-55 (complaint to the board of review), 200/12-10 (publication of the assessment list), 200/16-110 and 200/16-115 (Cook County township deadlines), 200/16-160 (appeal to the Property Tax Appeal Board), 200/9-145 and 200/9-150 (valuation at 33 1/3% and the classification exception), with 5 ILCS 70/1.11 (Statute on Statutes) and the Illinois Department of Revenue's published appeal steps ↗State legislature
Run it against the official tool: Illinois Department of Revenue — Property tax appeals ↗
🎓 Understand this tool
What it is
A calculator for the two numbers an assessment appeal actually turns on: how far your assessed value sits above comparable sales, and what a reduction would be worth at your local rate. It also puts the published cost of each route to that reduction beside the saving it would produce.
How it works
The comparison uses the MEDIAN of the comparable sales you enter rather than the average, because comparable sales are a small sample and one unusual transaction — a teardown, a family transfer, a distressed sale — drags an average badly. Assessing authorities reason in medians for the same reason. Where a state assesses at a fraction of market value rather than the whole, the assessed figure is divided by that ratio first so the two sides of the comparison are measured the same way. The saving is the reduction multiplied by the combined rate per hundred dollars of value, which is the form counties publish rates in.
Getting the most from it
- Take the assessed value and the rate straight off your notice and your bill — not from memory.
- Enter several recent sales of genuinely similar properties nearby. Three is a realistic minimum; one comparison is easy to dismiss.
- Leave out distressed sales, family transfers and teardowns. Including one weakens the rest of the list rather than lengthening it.
- Check your county deadline before doing anything else. A window that has closed ends the appeal whatever the numbers say.
Reading your result
A gap under about five percent is usually treated as within tolerance — valuation is approximate by design, and authorities expect to be roughly rather than exactly right. A larger gap is the argument, but it is an argument you still have to make with evidence. The saving figure assumes the reduction is granted in full, which is why it is shown as a range: meeting halfway is a common outcome.
What it can't tell you
This cannot tell you whether your comparables are genuinely comparable, whether your county assesses the way you think it does, how a particular review board tends to decide, or whether an appeal risks drawing attention to something else about the property. It does not file anything, and it is not a valuation. A licensed appraiser values property; a lawyer advises on appeals.
Frequently asked questions
Compare the assessed value against recent sales of genuinely similar properties nearby. If the assessment sits meaningfully above the median of those sales, that gap is the argument. A difference of a few percent is usually treated as within tolerance — valuation is approximate by design.
Change alerts — when a state revises the guideline or deadline behind this page
One email when the numbers change. Double opt-in, no spam, unsubscribe anytime.