Many of you may have already paid the second installment of the Cook County 2025 property tax bill, which was due on October 1. However, it's surprisingly common to realize after payment that the exemption section in the bottom left of the bill was left blank.

This second bill was issued nearly two months later than originally scheduled. Due to delays in the county's computer system upgrade, it was only available online in mid-August, and mailed around September 1.

When schedules are delayed, there's less time to carefully review the bill. If you only checked the amount and paid right away, I recommend taking another look now.

The area to check is the bottom left of the bill. The assessor's office indicates that you can see what exemptions were applied in this section.

The most basic exemption is the homeowner exemption. If you live in the home, you likely qualify, which deducts $10,000 from the equalized assessed value (EAV).

If you are over 65, a senior exemption is added. This further deducts $8,000 from the assessed value, so if both exemptions are missing, the difference can be significant.

Additionally, there are senior freezes for seniors with household incomes below $65,000, as well as exemptions for disabled individuals and disabled veterans. If you qualify but it's not indicated on your bill, there's a good reason to check.

The official process to reclaim missing exemptions is called a Certificate of Error, commonly referred to as a Certificate of Error application. You can submit this online on the assessor's office website under the certificates-error page, or visit in person after making an appointment.

The range of exemptions you can reclaim includes the 2025, 2024, 2023, and 2022 tax years. The key point is that you can address not only this year's bill but also those from previous years.

For reference, the deadline for applying for the 2025 tax year exemption was May 15, 2026. Applications submitted after this date will be processed as Certificates of Error rather than regular applications.

When applying, you will need identification and documents proving residency. A list of accepted photo IDs and documents is organized on the assessor's site, so it's best to review and prepare in advance.

The outcomes will fall into two categories. If the timing is right, you will receive a corrected bill reflecting the exemption, and you will only need to pay the reduced amount. If you have already paid, you will receive a refund.

At this point, most outcomes will be refunds. The assessor's FAQ states that the treasurer's office processes refunds within 6 to 8 weeks after application.

If you pay taxes through a mortgage escrow, there's one more thing to keep in mind. The assessor advises sending a copy of the corrected bill or the approved Certificate of Error to your mortgage company.

If you forget this step, it can be confusing to track where the refund goes and how the escrow amount is adjusted for the following year. Sending this one document can help reduce future confusion.

There may still be some who have not yet paid the second installment. Applying for an exemption does not delay your payment obligation.

Fortunately, late interest rates have decreased compared to previous years. Starting from the 2023 tax year, the rate has dropped from 1.5% per month to 0.75%, and this rate applies to the current 2025 tax bill as well.

However, since interest accrues monthly, the longer you delay, the more you lose. If paying all at once is difficult, check the payment plan calculator on the treasurer's website first.

Separately from exemptions, there may also be instances of double payments or overpayments from the past. You can check for overpayments on the treasurer's website at cookcountytreasurer.com using your PIN.

While exemption omissions and overpayments may seem similar, they are handled by different offices. Exemption omissions are managed by the assessor's office, while overpayment refunds are handled by the treasurer's office.

It's also convenient to separate your points of contact. For refund status, contact the treasurer's office at 312-443-5100, and for exemption applications, reach out to the assessor's office at 312-443-7550.

Common cases of omissions seen in the field are generally similar. Missing exemptions often occur in the first year of a new home purchase, when ownership changes, or when ownership is transferred to a trust.

While senior exemptions are typically automatically renewed once received, they can sometimes be omitted if the homeowner exemption is missed. If you are managing your parents' property tax bills, it's advisable to check this as well.

For those unfamiliar with English bills, it can be difficult to determine eligibility just by looking at the exemption names. In such cases, it's more reliable to enter your PIN on the assessor's site and check your exemption history.

Personally, I believe that even missing just the homeowner exemption is worth applying for. Opportunities to retroactively claim four tax years are rare.

Conversely, if your eligibility is unclear, it's better to consult the assessor's office before applying rather than forcing an application. Requirements for residency or income can vary based on individual circumstances, so it's safest to confirm with an expert.

In summary, the steps are straightforward. Check the bottom left of the bill, apply for a Certificate of Error if exemptions are missing, and if you have escrow, send a copy to your mortgage company.

This article is based on notices from the Cook County Assessor and Treasurer's offices as of the end of October 2026. Procedures may change, so please verify on the official site before applying.