Travis Bunn

Founder, AppealDesk · Published February 28, 2026 · Updated March 17, 2026

Illinois Property Tax Appeal Deadlines 2026: Cook County & Beyond

Updated March 2026

Illinois property tax deadlines are complex. Unlike states with one deadline, Illinois has rolling deadlines by township and county. Miss your window and you wait until next year.

Cook County Property Tax Appeal Deadlines 2026

The most common myth about Cook County is that you can only appeal in your reassessment year. That is not how it works. Under the Illinois Property Tax Code you can appeal every year, in every township, no matter where you sit in the triennial cycle. Your township opens once a year at the Assessor and again at the Board of Review, and both are real appeals.

What the triennial cycle controls is when the county recalculates your value, not when you are allowed to challenge it.

The Cook County Triennial Cycle

• 2024: City of Chicago townships reassessed
• 2025: North and northwest suburban townships reassessed (Barrington, Elk Grove, Evanston, Hanover, Maine, New Trier, Niles, Northfield, Palatine, Schaumburg, Wheeling)
• 2026: South and west suburban townships reassessed

If you are in a south or west suburban township, 2026 is your reassessment year: your value is being recalculated and your notice arrives this year. If you are in Chicago or the north suburbs, your value carries over from your last reassessment, and you can still appeal it this year if it is too high.

The 2026 Townships (South and West Suburbs)

These are the townships in the 2026 reassessment group, per the Cook County Assessor's appeal calendar:

• West: Berwyn, Cicero, Lyons, Oak Park, Proviso, River Forest, Riverside, Stickney
• Southwest: Lemont, Orland, Palos, Worth
• South: Bloom, Bremen, Calumet, Rich, Thornton

Each of these opens and closes on its own date rather than a single county deadline, and the Assessor publishes those dates township by township as the year moves. Several of the 2026 townships have already closed at the Assessor by late summer while others are still open or not yet scheduled, so a date you read in an article written in January is not a date to rely on in August. Check the calendar for your own township.

Worth repeating, because this is where most Cook County homeowners give up too early: if your Assessor window has already closed, you have not missed the year. The Board of Review opens your township separately, on its own schedule, after the Assessor closes it.

For the rest of the Cook County process, including how the triennial groups work, what evidence the Board responds to, and how to file at each level, see our Cook County property tax appeal guide.

Your 2026 Appeal Windows

• Assessor appeal: 30 days from your township's notice mailing date. Townships open on a rolling schedule through the year.
• Board of Review appeal: opens after the Assessor closes your township, on its own published schedule. Available whether or not you appealed at the Assessor, and whether or not you were reassessed this year.

Because both windows are township specific and rolling, the only reliable way to find yours is to look up your township on the Cook County Assessor's appeal calendar. What does not change is the underlying question: whether the value they are carrying is higher than what comparable homes actually sold for.

Other Illinois County Deadlines

DuPage County

• Notice Date: Early June 2026
• Appeal Deadline: 30 days from notice
• Board of Review: August-September 2026

Lake County

• Notice Date: May 2026
• Appeal Deadline: 30 days from notice
• Board of Review: July-August 2026

Will County

• Publication Date: June 2026
• Appeal Deadline: 30 days from publication
• Board of Review: September-October 2026

Kane County

• Notice Date: June 2026
• Appeal Deadline: 30 days from notice
• Quad Year: Every 4 years by township

Critical: Your Notice Date Sets Your Deadline

Illinois doesn't have one universal deadline. Your 30-day window starts when YOUR notice is mailed.

Track these dates:

• Notice mailed date (on the envelope)
• 30 calendar days from that date
• Board of Review dates (second appeal level)

Miss the Assessor window by even one day and that window is gone. It is a hard date, not a soft one. What it does not do is end your year, because the Board of Review opens on its own separate schedule afterward.

Illinois Two-Level Appeal Process

Level 1: Township Assessor

• File within 30 days of notice
• Informal process
• Can often resolve without hearing

Level 2: Board of Review

• Opens on its own schedule after the assessor closes your township
• Available whether or not you filed at Level 1
• More formal process
• Final county-level appeal

Both levels have strict deadlines, and they are separate deadlines. Missing Level 1 does not forfeit Level 2. This is the single most useful thing to know about appealing in Cook County, because the assessor window is short and easy to miss, and most people who miss it assume they are finished for the year.

Special Illinois Appeal Situations

Recent Purchase Appeal

Bought in the last 3 years? You may appeal even in non-reassessment years if:

• Purchase price was less than assessed value
• Arm's length transaction
• File within 90 days of purchase

Vacancy/Disaster Appeal

Property vacant or damaged? Special appeal rights exist outside normal cycle.

COVID Assessment Appeals

Some counties still accepting COVID-impact appeals for commercial properties.

Cook County Multiplier Alert

Cook County applies an equalization factor (multiplier) after appeals. Your final tax depends on:

1. Assessed value (what you appeal)
2. State multiplier (can't control)
3. Local tax rates (can't control)

Focus on #1, it's your only leverage point.

What Happens If You Miss Your Township's Window?

Consequences:

• Wait 3 years for next reassessment
• Pay inflated taxes the entire time
• No retroactive relief
• Thousands in unnecessary taxes

Example: $30,000 over-assessment = $750/year extra. Over 3 years = $2,250 lost forever.

How to Find Your Exact Deadline

1. Check your assessment notice, deadline is printed on it
2. Visit your county assessor website, most post deadline calendars
3. Call your township assessor, they'll tell you exactly
4. Don't guess, Illinois deadlines are unforgiving

Illinois Appeal Success Factors

What wins in Illinois:

• Recent comparable sales (last 12 months)
• Properties within same township
• Similar square footage and features
• Professional presentation

Unique to Illinois:

• Multipliers affect everyone equally
• Focus on base assessment accuracy
• Uniformity arguments very effective

Quick Illinois Action Steps

If You're in a 2026 Reassessment Township:

1. Now: Monitor mail for notice
2. Upon receipt: Mark deadline on calendar
3. Week 1: Gather comparable sales
4. Week 2: File appeal (don't wait)
5. Week 3-4: Prepare evidence

If You're NOT in a 2026 Reassessment Township:

1. Now: Pull your current assessed value and compare it against recent sales nearby
2. Find your window: you can still appeal this year, at the Assessor when your township opens and again at the Board of Review
3. If the number is high: file this year rather than waiting for your next reassessment
4. Either way: check your property record for square footage and room count errors

Don't Navigate Illinois Deadlines Alone

Illinois' township-by-township system is intentionally complex. Counties benefit when you miss deadlines.

AppealDesk handles Illinois appeals with:

• Township-specific deadline tracking
• Cook County multiplier explanations
• Comparable sales from YOUR township
• Both assessor and Board of Review forms
• Step-by-step township filing guides

Final Warning on Illinois Deadlines

30 days means 30 days. Not 31. Not "postmarked by." Received by Day 30.

Illinois counties reject thousands of appeals annually for being one day late. Don't add to that statistic.

Your notice is coming (or already arrived). Your deadline is set. What you do next determines whether you save money or donate it to your county.

The clock is ticking. Act now.