How to Appeal Your Property Tax in Illinois: Step-by-Step Guide
If you’re an Illinois homeowner, there’s a better than even chance your property is over-assessed. Cook County’s assessment system has been widely criticized for inaccuracy and regressivity, and even outside Cook County, assessors rely on mass-appraisal models that frequently miss property-specific factors like deferred maintenance, unfavorable locations, or functional obsolescence. Use our estimate maintenance costs for detailed numbers. The good news: Illinois has a structured appeal process, and success rates are higher than most people expect — around 30–40% of Cook County appeals result in reductions.
This guide walks you through every step of the appeal process, from evaluating whether your assessment is too high to filing at the county level and escalating to the Illinois Property Tax Appeal Board (PTAB) if needed.
Step 1: Understand Your Assessment
Before you can appeal, you need to understand what you’re appealing. Your property tax bill is based on three components:
| Component | What It Is | Can You Appeal It? |
|---|---|---|
| Assessed Value (AV) | The assessor’s estimate of market value × assessment ratio | Yes — this is what you appeal |
| Equalizer (State Multiplier) | Applied to bring assessments to statutory 33.33% level | No — set by state |
| Tax Rate (Levy) | Total of all taxing district rates combined | No — set by taxing bodies |
You can only appeal the assessed value — the assessor’s estimate of what your property is worth. You cannot appeal the tax rate or the equalizer.
How to Check Your Assessment
- Find your property’s assessed value on your county assessor’s website (Cook County Assessor at cookcountyassessor.com; other counties have their own sites)
- In Cook County: multiply your assessed value by the equalizer (approximately 2.9) to get your Equalized Assessed Value (EAV). Then subtract exemptions to get your net taxable value.
- In other counties: your assessed value should be 33.33% of fair market value. Multiply your AV by 3 to get the implied market value the assessor is using.
- Compare this implied market value to recent comparable sales in your area.
Step 2: Gather Comparable Sales Evidence
The strongest evidence for a property tax appeal is comparable sales — recent sales of similar properties at lower prices than your assessed value implies. Here’s what makes a strong comparable:
| Factor | Ideal Comparable | Acceptable |
|---|---|---|
| Distance | Within 0.5 miles | Within 1 mile |
| Sale Date | Within 6 months | Within 12 months |
| Size | Within 10% of your home’s sq ft | Within 20% |
| Bedrooms/Baths | Same count | ±1 bedroom or bath |
| Age | Within 10 years | Within 20 years |
| Condition | Similar | Adjustable |
You need at least 3 comparable sales, ideally 5–6. Sources for comp data include:
- Your county assessor’s website (most list recent sales)
- Zillow, Redfin, or Realtor.com (sold listings)
- Your real estate agent (if you have one)
- The Illinois Department of Revenue’s property transfer declarations
Step 3: File at the County Level
Cook County Process
Cook County has a unique two-step process:
Step 3A: File with the Cook County Assessor
- Wait for your township’s reassessment notice (Cook County reassesses on a triennial cycle — City of Chicago, north suburbs, and south suburbs rotate)
- File a complaint online through the Cook County Assessor’s website within 30 days of the reassessment notice
- Submit your comparable sales, photos of any property defects, and a written argument for why your assessment is too high
- The Assessor’s office reviews and issues a decision, typically within 2–4 months
Step 3B: Appeal to the Cook County Board of Review
- If the Assessor denies your complaint or the reduction is insufficient, you can appeal to the Board of Review
- Filing is done online at the Board of Review’s website during the township’s appeal window
- You can submit new evidence and request an oral hearing
- The Board reviews evidence and issues a final county-level decision
- Board of Review appeals have a higher success rate than Assessor complaints
Non-Cook County Process
Outside Cook County, the process is more straightforward:
- File a complaint with your county’s Board of Review within 30 days of receiving your assessment notice (typically mailed in the spring)
- Submit comparable sales evidence and any documentation of property defects
- Attend a hearing if requested (many counties allow evidence review without a hearing)
- The Board issues a decision, typically within 60–90 days
Step 4: Escalate to PTAB (If Needed)
If you’re unsatisfied with your county’s decision, you can appeal to the Illinois Property Tax Appeal Board (PTAB) — a state-level body that reviews property tax appeals from all 102 counties.
| PTAB Filing Detail | Requirements |
|---|---|
| Filing Deadline | 30 days after Board of Review decision |
| Filing Fee | $50–$100 depending on property value |
| Evidence Required | Comparable sales, appraisals, photos |
| Hearing Format | Formal hearing with testimony (in Springfield or by video) |
| Decision Timeline | 6–18 months (backlog varies) |
PTAB appeals are more formal than county-level appeals and may warrant hiring a property tax appeal attorney. If the reduction you’re seeking is significant ($2,000+ per year), the attorney’s contingency fee (typically 30–40% of first year’s savings) is often worth it.
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Step 5: Consider Hiring a Property Tax Attorney
Property tax appeal attorneys and firms handle the entire process for you — filing, evidence gathering, hearing representation, and follow-up. Most work on contingency, meaning you pay nothing upfront and they take a percentage of your savings.
| Fee Structure | Typical Terms |
|---|---|
| Contingency Fee | 30–40% of first year’s tax savings |
| No Savings = No Fee | Standard — you only pay if they succeed |
| Multi-Year Engagement | Some firms file annually on your behalf |
For Cook County homeowners, using a professional is particularly common — the process is more complex, the stakes are higher (Cook County assessments tend to be less uniform), and attorneys have established relationships with the Assessor’s office and Board of Review.
Timeline and Deadlines by County
Missing the filing deadline is the most common reason homeowners don’t appeal. Here are the key deadlines for Illinois’ largest counties:
| County | Assessment Notice Mailed | Appeal Deadline | Where to File |
|---|---|---|---|
| Cook County (City of Chicago) | Varies by township (triennial) | 30 days from notice | Assessor’s Office (online) |
| Cook County (Board of Review) | After Assessor decision | 30 days from publication | Board of Review (online) |
| DuPage County | March–April | 30 days from notice | Board of Review |
| Lake County | March–April | 30 days from notice | Board of Review |
| Will County | April–May | 30 days from notice | Board of Review |
| Kane County | April–May | 30 days from notice | Board of Review |
| Sangamon County | May–June | 30 days from notice | Board of Review |
The assessment notice is the trigger — mark your calendar when it arrives. In Cook County, township reassessment dates rotate on a triennial cycle, so your appeal window opens once every three years at the assessor level (though you can appeal to the Board of Review annually). In other counties, you typically have one annual window.
DIY Appeal vs. Professional Representation
For straightforward overvaluation cases (your home’s assessed value clearly exceeds comparable sales), a DIY appeal is feasible and free. The Board of Review process in most counties is designed to be accessible to individual homeowners. Here’s when each approach makes sense:
- DIY appeal is best when: You have 3–5 clear comparable sales showing lower values, the overvaluation is straightforward, and the potential savings are moderate ($500–$1,500/year). Print your evidence, fill out the form, and file.
- Professional representation is best when: You’re in Cook County (the process is more complex and political), the potential savings exceed $2,000/year, your case involves uniformity arguments rather than just comparable sales, or you’ve been denied at a previous level and want to escalate to PTAB.
Property tax appeal firms and attorneys in Illinois typically work on contingency — they take 30–40% of the first year’s savings and nothing if they don’t reduce your bill. The largest Cook County firms (Kensington Research, Morreale Law, and others) handle thousands of appeals annually and have established relationships and data that improve outcomes. The contingency model means there’s no financial risk to hiring a professional — you only pay if they save you money.
Common Grounds for Appeal
- Overvaluation: The assessor’s implied market value exceeds what your home would actually sell for, based on comparable sales. This is the most common and strongest argument.
- Lack of uniformity: Similar homes in your area are assessed at lower values per square foot. This argument is particularly effective in Cook County, where assessment uniformity has been well-documented as poor.
- Property defects: Structural problems, foundation damage, environmental contamination, or other physical defects that reduce value but aren’t reflected in the assessment.
- Errors in property record: Incorrect square footage, wrong number of bedrooms/bathrooms, incorrect lot size, or wrong property classification. These factual errors can be corrected without a formal appeal in many cases.
Knowing your assessment is the first step to knowing if you’re overpaying. Use our estimate your property taxes to estimate what your taxes should be based on your home’s fair market value. For a full explanation of how Illinois property taxes work, read our guide on Illinois property taxes explained.
What Happens After a Successful Appeal
If your appeal is granted, here’s what to expect for the financial impact and timeline:
- Reduction applies immediately for the current tax year. Your next bill will reflect the lowered assessment. In Cook County, this takes effect on the second installment bill; in other counties, it may appear on the next full bill.
- Refund for overpayment: If you already paid based on the higher assessment, you’ll receive a refund or credit on your next bill. Cook County processes these refunds through the county treasurer, typically within 2–4 months of the Board of Review decision.
- Escrow adjustment: If your lender escrows property taxes, notify them of the reduction. The lender should reduce your monthly payment to reflect the lower tax bill. If they don’t adjust automatically, call the escrow department with your new assessment notice.
- Reduction duration: The lowered assessment stays in place until the next reassessment cycle. In Cook County (triennial cycle), a successful appeal could save you money for 3 years. In other counties (annual or quadrennial assessments), the duration varies.
- Future appeals: A successful appeal doesn’t prevent the assessor from raising your assessment at the next reassessment. Many Cook County homeowners file appeals every cycle as standard practice. There is zero penalty for filing repeatedly, and the savings compound over time.
For a homeowner saving $1,500 per year through a successful appeal that lasts 3 years (one Cook County triennial cycle), the total savings is $4,500 — minus the attorney’s contingency fee of $450–$600 (30–40% of the first year’s savings) if you used professional representation. The net benefit of $3,900–$4,050 over three years makes the appeal well worth the effort. Learn how exemptions provide additional savings in our guide to getting the homeowner exemption.
Compare With Other States
Considering other markets? Here’s how other states compare:
- How to Appeal Your Property Tax in Alabama: Step-by-Step Guide
- How to Appeal Your Property Tax in Missouri: Step-by-Step Guide
- How to Grieve Your Property Tax in New York: Step-by-Step Guide
Compare With Other States
Considering other markets? Here’s how other states compare:
- How to Appeal Your Property Tax in South Carolina: Step-by-Step Guide
- How to Appeal Your Property Tax in Maryland: Step-by-Step Guide
- How to Appeal Your Property Tax in New Mexico: Step-by-Step Guide
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Frequently Asked Questions
How often can I appeal my property tax in Illinois?
You can appeal every year in most counties. In Cook County, appeals are filed during the reassessment year for your township (triennial cycle), but the Board of Review accepts appeals annually. Filing every year is common and doesn’t carry any penalty or negative consequence.
What is the success rate for property tax appeals in Illinois?
In Cook County, approximately 30–40% of appeals result in a reduction. Success rates vary by township and the quality of evidence presented. Outside Cook County, success rates are similar or slightly lower. Appeals with strong comparable sales evidence and/or professional representation have the highest success rates.
How much can I save by appealing?
Savings vary widely. The average successful Cook County appeal reduces the assessed value by 10–15%, which translates to $500–$2,000 per year in tax savings on a typical home. Some appeals — particularly those involving errors or significant overvaluation — save $3,000–$5,000+ per year. The reduction stays in effect until the next reassessment, so savings compound over the assessment cycle.
Should I hire a property tax attorney?
For Cook County homeowners with tax bills over $5,000, hiring a professional on contingency (30–40% of first year’s savings) usually makes sense. You pay nothing if they don’t save you money, and their expertise in evidence presentation and system knowledge typically produces larger reductions than DIY appeals. For simpler appeals in non-Cook counties, doing it yourself is feasible with good comparable sales evidence.
Will appealing increase my taxes?
No. An appeal can only reduce your assessment — the Board of Review and PTAB cannot raise your assessment as a result of your appeal. The worst outcome is that your appeal is denied and your assessment remains unchanged. There’s no risk to filing. Use our calculate monthly costs to see how a reduced tax bill would affect your monthly housing payment.