State Guide

How to Appeal Your Property Taxes in Illinois (2026 Guide)

Published July 12, 2026

If you own a home in Illinois, your township or county assessor sets its value, and that number drives your tax bill. Every year you have a window to challenge it — but Illinois is one of the more complex states, with rolling deadlines, a two-level local process, and its own assessment-level math.

The Illinois deadline: rolling, by township and county

Illinois has no single statewide appeal deadline. In Cook County, the assessor reassesses and opens appeals township by township, giving you roughly 30 days after your township's reassessment notice to file with the Assessor's office; the Cook County Board of Review then opens its own appeal window township by township. In the other 101 counties, you appeal to your county Board of Review, generally due 30 days after the county publishes its assessment list in the local paper.

Because the timing is rolling, the single most important thing is to check your township's or county's current window — on your notice, or on the assessor's or Board of Review's site — and file within it. If the Board of Review doesn't lower your value, the next rung is the state Property Tax Appeal Board (PTAB), heard de novo, or a circuit court tax objection.

How Illinois assesses your home

Illinois is not a full-value state, and the fraction depends on where you live. Cook County assesses homes at 10% of market value; the rest of Illinois assesses at 33⅓% (35 ILCS 200/9-145). A statewide equalizer (the "multiplier") is then applied to reach your equalized assessed value, which — after exemptions — your local tax rate hits. That machinery affects your bill, not the market value your appeal is really about: win a lower market value, and everything downstream drops with it.

Category	Illinois
Assessment basis	Cook County 10% of market value; rest of Illinois 33⅓% (35 ILCS 200/9-145)
Appeal deadline	Rolling — ~30 days after your township notice (Cook) or the county's published assessment list
Where you file	County Board of Review (Cook: Assessor, then Board of Review) → PTAB or circuit court
Assessment cap	None — Illinois has no acquisition or assessment-growth cap
Can the board raise your value?	Yes — with notice and a hearing; PTAB is de novo

Building your case

Illinois gives you two ways to win. The first is the standard one: your home's market value is too high, proven with recent, nearby comparable sales — homes like yours in size, age, and condition. The second is lack of uniformity — showing that similar homes near you are assessed at a lower level than yours (often measured in assessed dollars per square foot). Uniformity is a especially common winning path in Cook County, where assessment data is public and comparisons are straightforward. A strong appeal often leans on both angles.

One Illinois-specific caution: your county Board of Review can raise your assessment on your own appeal — but only after written notice and a hearing (35 ILCS 200/16-55 downstate; 35 ILCS 200/16-120 in Cook County) — and in Cook County a taxing district can also push for an increase. If you escalate to PTAB, the case is heard de novo, where the assessor or a taxing body can argue for a higher value. Increases on ordinary homes are uncommon but real, so file only when your evidence clearly supports a lower value.

Filing at the county level

Illinois runs appeals county by county (and, in Cook, township by township), and the mechanics — where and how to file, online portals, and the exact rolling deadlines — vary widely across all 102 counties. We're building out county-specific guides with the filing office and local calendar for each. In the meantime, use PROppeal to pull licensed comparable sales for your address and confirm your current window with your assessor or Board of Review.

Get your case built

You don't need to wait on a county-specific guide to start. PROppeal pulls licensed comparable sales for your address, works from your home's market value (not the confusing equalized-assessed-value math on your bill), and gives you a straight answer on whether your assessment is out of line — in time for your township's or county's rolling deadline.

Property tax rules and deadlines vary by jurisdiction and can change — verify with your county before relying on this.