How do I appeal my property taxes in Illinois?

File an appeal with your township or county assessor within 30 days of receiving your assessment notice. Submit comparable sales of similar homes that sold for less than your assessor's implied value. If unsuccessful, escalate to your county's Board of Review, then the Illinois Property Tax Appeal Board (PTAB) if needed.

How much can I save by appealing my Illinois property taxes?

Savings vary widely depending on the degree of over-assessment. Successful appeals in Illinois suburbs can reduce assessed values by 5–20%, translating to annual tax savings of several hundred to several thousand dollars depending on your tax rate and home value.

What is the deadline to appeal property taxes in Illinois?

Deadlines vary by county and township. Most assessor-level appeals must be filed within 30 days of the assessment notice mailing. Board of Review deadlines are typically in the fall. Check your specific county assessor's website for current-year deadlines — missing the window means waiting until the next reassessment cycle.

Can a new home buyer appeal property taxes in Illinois?

Yes. New buyers can appeal at any time during the open appeal window. Your purchase price is strong evidence of market value. If the assessed value implies a higher market value than you paid, you have a solid basis for appeal — especially if comparable sales also support a lower value.

Illinois Property Tax Appeal Guide: How to Fight an Inaccurate Assessment

Illinois has some of the highest property taxes in the United States — and many homeowners are overpaying because their assessed value is wrong. The property tax appeal process exists specifically to correct inaccurate assessments, and it’s more accessible than most homeowners realize. This guide walks you through how Illinois property taxes work, how to identify if you’re over-assessed, and exactly how to file an appeal.

How Illinois Property Taxes Work

Your property tax bill is determined by two things: your property’s assessed value and the tax rate applied by your local taxing bodies (school district, municipality, park district, etc.). In Illinois:

Properties are assessed at 33.33% of market value in most Illinois counties
Cook County uses a tiered system — residential properties are assessed at 10% of market value (before equalization)
The equalization factor (multiplier) adjusts assessments to bring them in line with state targets
Your tax bill = (Assessed Value × Equalization Factor − Exemptions) × Tax Rate

The key lever you control is your assessed value. If it’s too high relative to your home’s actual market value, you’re overpaying — and an appeal can fix it.

How to Tell If You’re Over-Assessed

The simplest check: compare your assessed value to recent sales of similar homes in your area.

Look up your property’s assessed value on your county assessor’s website
Multiply by 3 (for most counties) or by 10 (for Cook County, before equalization) to estimate the implied market value the assessor is using
Compare that implied value to actual recent sales prices of comparable homes (similar size, age, condition, and neighborhood)
If the assessor’s implied market value is significantly higher than what comparable homes are actually selling for, you likely have grounds for an appeal

You can find comparable sales through your county assessor’s website, the Illinois Property Tax Appeal Board (PTAB) database, or by asking a local real estate agent to pull recent comps — the same data used in a home appraisal.

The Illinois Property Tax Appeal Process

Illinois offers multiple levels of appeal, each with its own deadlines:

1. County Assessor Appeal

The first level of appeal is filed directly with your township or county assessor. Deadlines are typically 30 days from when your assessment notice is mailed — check your county assessor’s website for the exact window. This is the simplest, cheapest, and fastest level of appeal.

2. Board of Review Appeal

If the assessor doesn’t reduce your value sufficiently, you can appeal to your county’s Board of Review. In Cook County, this is the Cook County Board of Review. In Will County, it’s the Will County Board of Review. Deadlines vary by township and year — typically in the fall.

3. Illinois Property Tax Appeal Board (PTAB)

If the Board of Review doesn’t provide relief, you can escalate to the state-level PTAB. PTAB appeals are more formal, take longer (often 1–3 years), and involve submitting a written complaint with supporting evidence. For significant over-assessments, the savings can justify the wait.

4. Circuit Court

The final level is a circuit court challenge — used primarily for commercial properties or when the dollar value of the dispute justifies litigation costs.

What Evidence to Submit

Strong appeals are built on evidence. The most persuasive evidence is:

Recent comparable sales: 3–5 sales of similar homes (same neighborhood, similar square footage, age, and condition) that sold for less than your assessor’s implied market value. Sales within the last 12–18 months carry the most weight.
Recent appraisal: A licensed appraisal supporting a lower value is strong evidence — particularly at the PTAB level.
Property record errors: Incorrect square footage, bedroom/bathroom count, lot size, or property characteristics in the assessor’s records can justify a reduction without any market evidence at all.
Photos of condition issues: Evidence of deferred maintenance, structural issues, or factors that reduce value relative to comps.

Cook County vs. Collar Counties

Cook County has its own distinct system with township-level assessors, a triennial reassessment cycle (each third of the county is reassessed every three years), and a separate Board of Review process. The Assessor’s MyDec system and the Board of Review’s online filing portal make Cook County appeals relatively accessible.

Will County and other collar counties follow a different assessment calendar and have their own Board of Review procedures. Check your specific county’s assessor website for current deadlines — missing a deadline means waiting until the next assessment cycle.

Should You Hire a Property Tax Attorney or Consultant?

For most residential appeals at the assessor or Board of Review level, homeowners can file successfully on their own using comparable sales data. The process is designed to be accessible to non-attorneys.

For higher-value properties, complex situations, or PTAB appeals, a property tax attorney or tax consultant who works on contingency (taking a percentage of the savings) can be worth it. You pay nothing if they don’t win a reduction.