Illinois Board of Review and Certificate of Error Guide

The two main paths this guide covers

Illinois property tax relief and correction issues often get mixed together. A homeowner may say, “My taxes are wrong,” but that can mean several things.

A Board of Review appeal is usually used when you believe the assessed value is wrong for the current assessment cycle. A Certificate of Error is usually a correction tool for an error after the tax year has moved farther along, especially when an exemption or assessment error was missed.

What an Illinois Board of Review appeal is

Each Illinois county has a local assessment system. The Board of Review reviews assessment complaints and can change assessments when the facts and evidence support a change.

The Illinois Department of Revenue’s assessment appeals guidance is clear on one point: in an assessment appeal, you are appealing the assessed value of the property. You are not appealing the tax rate. You are not appealing the total bill just because it is high.

This matters because a tax bill can rise for more than one reason. The Board of Review usually focuses on whether the assessment is correct.

When a Board of Review appeal may make sense

A Board of Review appeal is most useful when you can point to facts. The strongest appeals are usually not emotional. They are built around documents, property records, comparable homes, sales, or a clear mistake.

Common reasons to look at an appeal include:

• The assessor’s market value appears higher than what the property would reasonably sell for.
• Similar nearby properties are assessed lower than yours.
• The county property record has incorrect facts, such as square footage, lot size, building type, or condition.
• You recently bought the home in an arm’s-length sale for less than the county’s market value estimate.
• You have a professional appraisal that supports a lower value.
• The property had serious damage or a major condition problem that the assessment did not reflect.

The appeal is not mainly about hardship. It is not usually won by saying the bill is unaffordable. If the problem is income, age, disability, veteran status, or surviving spouse status, you may need an exemption, freeze, deferral, or other relief program instead of an assessment appeal.

Where Illinois homeowners usually start

Start local. Property assessment is handled county by county.

In many Illinois counties outside Cook County, the first informal contact is the township assessor, multi-township assessor, or supervisor of assessments. If the assessment books are still open, the assessing official may be able to correct an error before a formal appeal is needed.

If the issue is not fixed informally, the formal appeal is usually made in writing to the county Board of Review. The Illinois Department of Revenue says to contact the Board of Review for the county’s deadlines, complaint forms, evidence rules, and hearing procedures.

Cook County is different in size and process. The state Property Tax Appeal Board’s getting started page notes that Cook County taxpayers may file an appeal with the Cook County Assessor or the Cook County Board of Review. Cook County also uses township-based filing windows, so one homeowner’s filing period may be different from another homeowner’s filing period.

Evidence to gather before a Board of Review appeal

Before filing, gather the facts that show why the assessment is wrong. You do not need every item below in every case. But you should try to build a clean file before the deadline.

• Your Property Index Number, often called the PIN.
• The current assessment notice or property record card.
• Photos of your property, especially if condition is part of the issue.
• Photos and property record cards for similar properties, if you are comparing assessments.
• Recent comparable sales, with sale dates and sale prices.
• Your closing statement, deed, transfer declaration, or purchase contract if you recently bought the home.
• A professional appraisal, if you have one and it supports your position.
• Proof of factual errors, such as measurements, permits, demolition records, repair records, or other documents.

The Illinois Department of Revenue lists similar items in its appeal guidance, including property record cards, photographs, sale evidence, purchase documents, and appraisals. The point is simple: show the Board why the assessment is wrong, using evidence that can be checked.

The Board of Review process in plain English

Every county has its own forms and local rules. But the basic path usually looks like this:

1. Read the assessment notice. Look for the assessed value, property class, mailing date, and any appeal instructions.
2. Check the property record. Make sure the county has the right facts about the property.
3. Talk to the local assessing office early. If the issue is a simple error and the books are still open, the office may be able to correct it.
4. Find the Board of Review deadline. This deadline can vary by county, township, and assessment year.
5. File the correct written complaint or online appeal. Do not rely on a phone call as your appeal unless the office says in writing that it satisfies the filing requirement.
6. Upload or submit evidence. Follow the county’s format, page, hearing, and deadline rules.
7. Watch for notices. The Board may decide on documents, schedule a hearing, request more information, or issue a written decision.

If you still disagree after the Board of Review decision

If the county Board of Review issues a decision and you still disagree, you may have another path. The Illinois Department of Revenue says a taxpayer who does not agree with the Board of Review decision may appeal in writing to the State Property Tax Appeal Board or file a tax objection complaint in circuit court. The taxpayer must still pay the taxes while the appeal is pending.

The Illinois Property Tax Appeal Board, often called PTAB, is a state board that hears property assessment disputes. PTAB says its jurisdiction is limited to deciding the correct assessment based on equity and the weight of the evidence. PTAB does not review the amount of the tax bill, the tax rate, or whether property should be exempt from taxation.

PTAB’s official getting started guidance says a petition to PTAB must be filed within 30 days of the county Board of Review’s written decision, or within 30 days of written notice of final adopted township multipliers by the Board of Review. Check the current PTAB instructions before filing because e-filing rules and required documents can change.

PTAB’s forms and brochures page says certain appeals must be e-filed, and its filing page says a separate petition is needed for each assessment year.

What a Certificate of Error means in Illinois

A Certificate of Error is not the same thing as a regular Board of Review appeal. It is a correction tool. It is used when an assessment or exemption error needs to be corrected after the normal assessment process has moved forward.

Illinois law treats Cook County and counties under 3,000,000 people differently. For Cook County, the main Certificate of Error statute is 35 ILCS 200/14-15. For counties with fewer than 3,000,000 people, the related statute is 35 ILCS 200/14-20.

For ordinary homeowners, the practical question is: “I missed an exemption, or the county made a mistake. Can it still be fixed?” The answer depends on the county, tax year, error type, and bill status.

Cook County Certificate of Error for missed exemptions

Cook County has the clearest public Certificate of Error process for many homeowners. The Cook County Assessor’s Certificates of Error page says Illinois law allows the Assessor to apply changes to a property tax bill that has already been issued. It describes the process as a way to correct the assessment after that tax year’s assessment is finalized.

Cook County lists two types of Certificates of Error:

• one for missing exemptions for past tax years; and
• one to correct a property’s assessed valuation after a tax bill has been issued.

For missed exemptions, Cook County’s page said, as checked on May 16, 2026, that homeowners could apply for certain missing homestead exemptions for tax years 2024, 2023, 2022, and 2021 if the homeowner was eligible in the tax year and the exemption was not applied to the paid bill. The page listed examples such as the Homeowner Exemption, Senior Exemption, Low-Income Senior Citizens Assessment Freeze Exemption, Persons with Disabilities Exemption, Veterans with Disabilities Exemption, and Returning Veterans Exemption.

Do not assume that a past exemption will be granted just because you have it now. Cook County says the property must have been eligible in the tax year for which the homeowner is applying. You may need a photo ID and documents that prove the home was your primary residence or that you met the exemption rules for that specific tax year.

Cook County says that during peak periods, Certificate of Error applications for missing exemptions may take 8 to 10 weeks for Assessor staff to process. If approved, the Treasurer’s Office mails refund checks within 3 to 4 weeks. If denied because documents are missing, Cook County says the homeowner may reapply with complete documents.

Cook County Certificate of Error for valuation problems

Cook County also has Certificates of Error for property-assessed valuation. This path can be more complicated. If the property’s assessment was previously reviewed by the Board of Review, the Board of Review must approve the Certificate of Error as well. Non-residential requests seeking a reduction of more than $100,000 in assessed value must be sent to the Circuit Court for a judge’s consideration.

Cook County offers a Certificate of Error status search for many valuation-based Certificates of Error. The tracker is not for exemption-related Certificates of Error and does not include every type of Certificate of Error. If an over-assessment Certificate of Error has already been issued and certified, the Cook County Treasurer has a Certificate of Error refund form.

Certificate of Error outside Cook County

Outside Cook County, do not assume Cook County’s online process applies. The law for counties with fewer than 3,000,000 people is different, and each county may have its own instructions.

Illinois law for counties under 3,000,000 people addresses certificates for assessment errors, other than judgment calls about valuation, and also refers to a certificate of error when an owner failed to file for a homestead exemption during the previous assessment year and qualified for it.

That does not mean every late issue can be fixed at any time. It means you should ask the county assessment office or Board of Review a very specific question: “Is there a Certificate of Error or other correction process for this tax year and this type of mistake?”

How to choose the right path

Use the current status of your problem to decide what to ask about first.

If you are late

If the Board of Review filing window is closed, do not guess. Call or message the official office. Ask whether any of these options still exist:

• a correction by the assessor because the books are still open;
• a Certificate of Error for a missed exemption or other specific error;
• a PTAB appeal, if you already received a Board of Review decision and are still within the PTAB deadline;
• a circuit court tax objection path, if appropriate and timely; or
• a new appeal in the next assessment year.

Being late on an assessment appeal does not always mean nothing can be fixed. But it may mean the regular appeal route is closed for that year. It may also mean the tax bill still must be paid while you pursue a correction or appeal.

If your appeal or Certificate of Error is denied

Read the denial carefully. Do not throw it away. The letter or online notice may tell you whether the problem was missing documents, ineligibility, weak valuation evidence, a filing deadline, or the wrong process.

If the denial was due to missing documents, ask whether you can reapply or supplement the file. Cook County’s Certificate of Error page says a homeowner denied for missing documentation may reapply with complete documents. Other counties may have different rules.

If a Board of Review appeal was denied and you still believe the assessment is wrong, check the PTAB and circuit court deadlines right away. PTAB’s deadline can be short. Do not wait until the bill is due to ask what review rights remain.

What renters and helpers should know

Renters usually do not file homestead exemptions or assessment appeals for a property they do not own. Family helpers can still gather the PIN, notices, tax bills, proof of residence, IDs, prior bills, and denial letters before calling the official office with the owner.

A careful call script

Keep notes with the date, office name, and person you spoke with.

Important differences between relief words

Illinois property tax terms can sound alike. An exemption removes or reduces taxable value under a specific rule. A freeze may limit how an assessed value changes, but it may not freeze the total bill. A deferral delays payment and can involve liens, interest, or repayment. A rebate or credit is separate from an assessment appeal. An assessment appeal challenges value or assessment facts. A Certificate of Error corrects certain mistakes after the normal process has moved forward.

Before you file anything

Confirm the county, township, PIN, current deadline, and official form. Save proof that you filed, including confirmation numbers, emails, mail receipts, or screenshots. Keep copies of every document you submit.