Step-by-Step Guide to Illinois Property Tax Appeals

O'Connor presents a step-by-step guide to Illinois property tax appeals.

CHICAGO, IL, UNITED STATES, April 1, 2026 /EINPresswire.com/ --


Whether in a rural town or the heart of Chicago, taxpayers all over Illinois are facing the heaviest property taxes in the nation. Thanks to numerous unresolved problems, including a statewide pension issue, taxes and property values continue to rise. While recent legislation has stalled, many Illinois taxpayers have been keeping the wolves at bay by using exemptions and property tax appeals. These two vital tools are a must in Illinois and have saved many homes and businesses from delinquent taxes or even becoming victims of a tax sale.

Appeals run on a strict deadline schedule, which starts after a county sends out notices of assessment. This makes understanding the assessment imperative to protest taxes or understand available exemptions. O'Connor will go over the various steps needed to appeal taxes in Illinois.

Step 1: Confirm When and How the Notice is Received

Illinois does not have a set time to send out assessment notices. While they are usually sent out during reassessment, each township across the state runs on its own timetable. In Cook County, reassessment notices are sent out every three years, following the triennial reassessment cycle. In other parts of Illinois, notices may be published or mailed annually. Because tax rates and valuations can change every year, it is often good practice for taxpayers to check their assessor’s database to make sure they are on top of any changes. Notices are usually mailed in the late summer or early fall. The deadline for appeals is likewise tied to the township, typically 30 days after the assessment is mailed or published. In Cook County, appeals directly to the Cook County Assessor’s Office (CCAO) have a deadline of 30 business days after publication or mailing.

Step 2: Review Property Details for Errors

If owners are looking to appeal, it is important to review the notice to see what has changed and what errors there might be. No matter what, the township assessor can make mistakes, and some can be extremely costly. When viewing the assessment, first make sure that the owner’s name is correct. Next, confirm that the classification of the property is right. Make sure the home is not listed as a business, for instance, as this mistake could raise taxes significantly. Ensure that the assessor also has the correct size and improvements listed.

Step 3: Verify Exemptions

While they do not appear on your assessment, owners should take time to ensure that exemptions are squared away. These are incredibly important, as they have a huge impact on the taxable value, which influences the overall tax burden. These can be found online with the assessor or on the tax bill. If any are missing, owners will need to file the exemptions promptly, or file a certificate of error to have an exemption applied if the deadline has already passed. In Cook County, exemptions are typically only applied on the second installment of property tax bills.

Step 4: Understand Your Market and Assessed Value

Once basic data has been confirmed, the next thing to look at is the market and assessed value for the property. Market value is what the home or business would be worth on the open market. This is determined by the assessor studying property sales trends for the past three years. This assessment is often placed on a property sight unseen, using computer models to apply market value to a property based solely on location and statistics. Assessments often use old information about both property details and the real estate market itself, often leading to inflated market values. If the assessment shows a large increase compared to the previous assessment, then that is usually an indicator that an appeal should be filed.

Assessed value takes the market figure and distills it down to a sum that can be taxed. One-third of the market value is used as the basis for taxes in Illinois, with the exception of Cook County, which uses only 10% for residential properties and 25% for commercial real estate. After this, the number is reduced further by exemptions and other reductions, producing the final base value. This value will then be multiplied by the equalization factor applied by the township or county to arrive at the equalized assessed value (EAV). Once established, the EAV can then be multiplied by various tax rates to create a tax bill.

Step 5: Decide Grounds to Appeal

After reviewing the values, owners will have to decide if they want to protest them or not. There are two ways to go about this. First, see if the market value seems reasonable. If it looks excessive when compared to the reality of the property, then that is a textbook reason to appeal. The notice should have a previous market and assessed values. If there was a large spike in value between the two assessments, then that is another red flag that should prompt an appeal. Another reason to focus on these values is to find unequal assessment. Under Illinois law, properties with similar characteristics, classification, and location should be assessed at similar levels relative to comparable properties.

When determining whether to appeal based on value, there are three main justifications:

A large increase from the year before

Value is higher than the sale prices for comparable properties over the past three years

Assessed value is higher than neighboring properties with similar characteristics, such as age or size

Step 6: Gather Evidence
If you plan to appeal, you’ll need to gather:

Comparable sales
Neighbor assessments and permanent index numbers (PIN)
Property documentation
To prove excessive valuation or assessment, you will need to find the records of property sales in your area dating back three years. The goal of this is to show that your home or business is worth less than the assessor’s estimated value. By comparing your assessment to neighboring properties with similar characteristics, you can demonstrate that you are being assessed more than the surrounding real estate.

While protesting your property values in Illinois is a right, proving that you deserve a reduction can be a challenge. While errors in size or ownership are easy to prove, gathering evidence related to excessive values or unequal assessment is a different story. The records noted above can take extensive research and time to complete. This is why many taxpayers in Illinois decide to leave the gathering of evidence to professionals.

Step 7: File Appeal Before the Deadline

The deadlines for appeals are determined by the township, so there is no central date to keep in mind. In Cook County, first option is to appeal the values with the township assessor, before making a more formal complaint with the Board of Review (BOR). Outside of Cook County, appeals are only officially made with the BOR, though owners can contact the assessor to attempt to negotiate a reduction. In Cook County itself, there are two deadlines, one for appealing to the assessor directly, and another reserved for the BOR. These multiple deadlines give the people of Cook several chances to land a reduction. The deadline for appeals is usually listed on the assessment notice. If owners are planning to appeal, they must do so before the deadline, as they are generally final, with limited exceptions.

About O'Connor:
O’Connor is one of the largest property tax consulting firms, representing 185,000 clients in 49 states and Canada, handling about 295,000 protests in 2024, with residential property tax reduction services in Texas, Illinois, Georgia, and New York. O’Connor’s possesses the resources and market expertise in the areas of property tax, cost segregation, commercial and residential real estate appraisals. The firm was founded in 1974 and employs a team of 1,000 worldwide. O’Connor’s core focus is enriching the lives of property owners through cost effective tax reduction.

Property owners interested in assistance appealing their assessment can enroll in O’Connor’s Property Tax Protection Program ™. There is no upfront fee, or any fee unless we reduce your property taxes, and easy online enrollment only takes 2 to 3 minutes.

Patrick O'Connor, President
O'Connor
+1 713-375-4128
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