Key Takeaways
Illinois property owners can appeal their assessment at three levels: the county assessor, the Board of Review (BOR), and the Illinois Property Tax Appeal Board (PTAB).
Cook County uses a triennial reassessment cycle with a roughly 40-day appeal window after notices are mailed, while the state's other 101 counties follow their own schedules.
Valid grounds for an appeal include overvaluation, lack of uniformity with comparable properties, and factual errors on the property record card.
The BOR cannot increase your assessed value as a result of filing an appeal, so there is no financial risk to challenging your assessment.
We handle the entire Illinois appeal process on a contingency basis: 25% in Cook County and 35% in the rest of the state, with no upfront cost.
Property taxes in Illinois rank among the highest in the nation. The median home in Cook County is valued at $210,000, yet the median annual tax bill reaches $4,680. That translates to an effective rate of 2.01%, nearly double the national median of 1.02%. If you own property in Cook County or anywhere in the state, learning how to file an Illinois property tax appeal can lead to meaningful savings.
Cook County's tax burden often grabs headlines, but collar counties like DuPage, Lake, and Will have effective rates that rival or exceed Cook County's.Â
Across the state, Illinois property tax rates rank well above the national average, with DuPage County consistently among the highest-taxed in the country.
For single-family investors managing multiple properties across the Chicago metro area, the cumulative impact of overassessment compounds quickly. Across a portfolio of even five to ten properties, a successful appeal on each one can recover thousands of dollars in annual tax savings.
Not sure if your assessment is too high? Find out in 60 seconds if you're overpaying.
Valid Grounds for Appealing Your Illinois Assessment
Not every high tax bill justifies an appeal. Illinois law requires you to demonstrate that something is wrong with the assessed value itself. Simply disagreeing with how much you owe is not a valid basis for challenging your assessment.
Three grounds support a formal appeal:
Overvaluation: The assessor placed your property's market value higher than what comparable sales in your area support. This is the most common and straightforward basis for an appeal.
Lack of Uniformity (Equity): Your property is assessed at a higher percentage of market value than similar properties in the same area. Even if the assessed value is technically accurate, it may be disproportionately high relative to your neighbors.
Factual Errors: The property record card contains incorrect information, such as wrong square footage, an inaccurate lot size, or a misclassified building type. These errors inflate the assessed value without reflecting reality.
For investors with multiple Illinois properties, uniformity appeals can be especially powerful. If one property in your portfolio is assessed at a noticeably higher rate per square foot than the others, that gap creates a strong case.
The Illinois Department of Revenue appeal guidelines outline each of these grounds in detail. Review them before filing so you know which argument best fits your situation.
How Much Are You Over Paying?
The Three Levels of an Illinois Property Tax Appeal
Illinois offers three levels at which you can challenge your property's assessed value. Each level builds on the one before it, and you must generally exhaust the prior level before moving forward.
County Assessor (CCAO in Cook County): Start here. The assessor's office often functions more like a negotiation than a formal proceeding. It is generally the easiest and fastest way to correct simple factual errors (e.g., incorrect square footage or number of bedrooms) or resolve minor valuation disputes.
Board of Review (BOR): If the assessor doesn't resolve the issue, file a formal complaint with your county's BOR. In Cook County, property owners get two separate opportunities to appeal: first to the Cook County Assessor's Office, then to the BOR. This Cook County two-appeal rule gives you two independent chances to reduce your assessed value each year.
Illinois Property Tax Appeal Board (PTAB): If the BOR decision is unfavorable, you can appeal to the Illinois Property Tax Appeal Board (PTAB). PTAB hearings are more formal, and cases can take 12 to 24 months to resolve.
Most property owners achieve results at the assessor or BOR level. For investors managing a portfolio, we can handle appeals across multiple counties simultaneously through our Illinois property tax appeal service.
Understand the Illinois Property Tax Appeal Process
Illinois releases property valuations on different schedules depending on where you are in the state. Cook County reassesses one-third of its parcels each year under a triennial cycle, while most of the other 101 counties reassess all properties annually or on their own multi-year schedules.
Cook County's triennial assessment system divides its 1.8 million parcels into three reassessment zones:
City of Chicago: Reassessed in 2024 and 2027
North Suburbs: Reassessed in 2022 and 2025
South and Western Suburbs: Reassessed in 2023 and 2026
Even during off-reassessment years, you can still file an appeal. Check your Cook County property taxes to see how your assessment compares to recent sales in your area.
Register Your Intent To Appeal With the County
As the most populous county in Illinois, Cook County has a different process from the rest of the state. Here are the Cook County and statewide appeal requirements:
Cook County: Notify the Cook County Assessor's Office or the Cook County Board of Review that you plan to appeal. The appeal window opens when Notices of Value are mailed for your township and lasts approximately 40 days. Missing this window means waiting until the next reassessment cycle.
Rest of Illinois: Contact your chief county assessment officer or local assessor. Some counties require a written complaint form; others accept informal contact. In all cases, you must eventually file a formal complaint with your county's Board of Review.
Missing a deadline may disqualify you from filing an appeal entirely. Timelines differ across the state, so contact your local county assessor's office as soon as you receive your notice.
Gather Evidence To Support Your Appeal
Once you've registered your intent, the next step is to gather evidence demonstrating that your property's assessment is incorrect. The Illinois Department of Revenue evidence requirements outline what the BOR considers. Strong evidence typically includes:
A copy of your property record card, along with photographs of your property
Comparable sales reports showing recent transactions for similar properties in your neighborhood
An independent appraisal of the subject property
Property record cards for comparable properties in the area
A copy of the purchase contract, deed, or Real Estate Transfer Declaration
For single-family investors, comparable sales data is your strongest tool. When you own multiple properties in the same township, you can cross-reference assessments across your own portfolio to identify outliers. Properties assessed at a higher rate per square foot than similar holdings reveal a uniformity argument.
The more evidence you compile, the stronger your case. After processing over a million appeals nationwide, we've found the difference usually comes down to three to five well-chosen comparable sales.
Conduct a Thorough Review of Your Property Tax Assessment
Understanding how Illinois calculates your tax bill is essential before filing. A 1975 law sets the assessment level at 33.33% of fair market value for most properties. The resulting figure, known as the Equalized Assessed Value (EAV), is what drives your tax bill.
Here is how that calculation works in practice:
Step | What Happens | Example ($300,000 Home) |
|---|---|---|
1. Market Value | Assessor estimates fair market value | $300,000 |
2. Assessment Level (33.33%) | Multiply by the statutory assessment ratio | $100,000 |
3. Equalization Factor | State applies a multiplier to ensure county-level uniformity | $100,000 x 1.00 = $100,000 |
4. Exemptions Applied | Homestead and other exemptions reduce the EAV | $100,000 - $10,000 = $90,000 |
5. Tax Bill | EAV x local tax rate | $90,000 x 6.5% = $5,850 |
In Cook County, the equalization factor (sometimes called the "multiplier") is set annually by the Illinois Department of Revenue. It can significantly shift your EAV up or down. See the IDOR assessment FAQ for current multiplier details.
You may also qualify for property tax exemptions in Illinois. The general homestead exemption reduces the EAV of your primary residence without affecting its market value. Senior, disabled veteran, and other exemptions may apply.
Review your property record card carefully. Errors in square footage, room count, or building classification are common and can inflate your assessed value. These mistakes are often the simplest to correct through an assessor-level appeal.
Document Any Property Improvements or Damage
County assessors rarely inspect properties in person. Their records may not reflect current conditions, which could result in your property being overvalued due to outdated or incorrect data.
Conditions that can lower your assessed value and the documentation you need for each:
Condition | Impact on Value | Evidence To Gather |
|---|---|---|
Storm or fire damage | Reduces market value | Photos, insurance claims, contractor estimates |
Deferred maintenance (roof, foundation, plumbing) | Reduces market value | Inspection reports, repair quotes, dated photos |
Assessor lists non-existent improvements | Inflates the assessed value | Photos showing actual condition, building permits (or lack thereof) |
Overestimated renovation quality | Inflates the assessed value | Interior photos, contractor statements |
Include all documentation in your evidence package when you file your Illinois property tax appeal. For investors with multiple properties, condition-based evidence is especially useful for older rental units where deferred maintenance directly affects market value.
Engage With County Officials During the Process
Most county officials want to work with you to keep the process accurate and efficient. In many cases outside Cook County, there is no formal hearing; you simply present evidence to the review board and discuss it. In some situations, you can reach an agreement with the assessor without the full board's involvement.
Prepare for the Hearing: What To Expect
What happens at your hearing depends on which level you've reached and which county you're in. At the BOR level in most counties, the board reviews your evidence, asks clarifying questions, and decides by majority vote.
In Cook County, most BOR appeals are decided on paper. The board reviews your written submission and comparable sales data without an in-person hearing. This makes the quality of your documentation even more critical.
If your case reaches the PTAB, expect more formal proceedings. PTAB hearings follow quasi-judicial procedures, with sworn testimony and stricter evidentiary standards. PTAB cases take significantly longer to resolve, often 12 to 24 months from filing to decision.
Present Your Case Effectively at the Hearing
Whether you're presenting in person or submitting on paper, preparation determines the outcome. The board's job is to evaluate whether the assessed value reflects the property's fair market value. Your argument should focus exclusively on that question.
Lead with comparable sales that show similar properties selling for less than your assessed market value. Board members respond to clean, well-organized data, not emotional arguments about how much you're paying.
For investors with multiple properties, presenting portfolio-level comp data can strengthen your case. If three of your five properties in a township are assessed at $180 per square foot, but two are assessed at $220, the inconsistency speaks for itself.
Timelines and Deadlines for Illinois Property Tax Appeals
Deadlines vary across Illinois's 102 counties. Missing your window means waiting an entire year, or in Cook County's case, potentially until the next triennial cycle. Contact your assessor's office to verify exact dates, but here is a general overview.
Cook County timeline:
Notices of Value are mailed on a rolling basis by township, typically between February and August
The appeal window opens when your township's notices are mailed and lasts approximately 40 days
The Cook County BOR publishes a separate schedule for complaint filings by township
BOR decisions are typically issued within several months of the filing deadline
Collar counties and downstate Illinois:
Assessments are usually sent out in the spring or early summer
Most counties offer a 30-day window to file an appeal with the Board of Review
Hearings generally take place in late summer or early fall
BOR decisions are issued within several weeks to a few months
PTAB timeline:
You must file a PTAB petition within 30 days of receiving the BOR decision
Review the PTAB filing requirements for specific documentation and formatting rules
PTAB hearings are scheduled on the board's calendar and can take 12 to 24 months from filing to resolution
Visit your county's website and watch for mail notices to stay current on exact timelines.
Common Mistakes To Avoid During the Appeal Process
The most common mistake is showing up without enough evidence. Collect comparable sales data, document property issues, and highlight any factual errors on the assessment. An independent appraisal can add credibility, but well-chosen comps are usually sufficient.
Focus your argument on the property's assessed value, not on how high your tax bill is. The BOR evaluates whether the assessment reflects fair market value. If the assessed value decreases, the tax bill will follow.
Do not confuse assessed value with market value. In Illinois, the assessed value is 33.33% of market value (in Cook County, it’s 10%), so your argument should address the underlying market value figure, not the assessed number alone.Â
In Illinois, the Board of Review cannot increase your assessment as a result of filing an appeal. There is no risk that your taxes will go up because you challenged the valuation. This is one of the most common concerns we hear from property owners, and it should not prevent you from filing.
Use Ownwell To Maximize Your Illinois Property Tax Savings
We manage the entire Illinois appeal process from start to finish. Our local tax experts build your evidence package, file the appeal with the correct county body, and handle all communication with the BOR or PTAB on your behalf.
Our pricing is straightforward and contingency-based: you pay nothing unless we lower your tax bill. In Cook County, our fee is 25% of the refund or savings.Â
In the rest of Illinois, it's 35% of the first year's savings.Â
Review Ownwell's pricing for Illinois appeals for full details and examples.
For single-family investors managing multiple properties, we offer a portfolio enrollment path. Enroll all of your Illinois properties at once, and we handle appeals across every county where you own property. Portfolio-level savings compound year over year as we maintain lower assessed values across your holdings.
Beyond appeals, Illinois homeowners and investors may qualify for exemptions that further reduce their tax bills.Â
Our Illinois homestead exemption guide covers eligibility and the application process. We also retroactively apply for missed homestead exemptions for up to 3 years.
Ready to stop overpaying? Ownwell's Illinois property tax appeal service takes less than three minutes to start, with no upfront cost and no risk.
