Cook County property taxes were due October 1. What the late charge is
Cook County property tax bills were due October 1, 2026. Here's how the 0.75% monthly late charge works, what counts as on time, and how to pay.
If you missed the October 1 deadline for your Cook County property tax bill, the late charge is 0.75% of the unpaid balance per month, or portion of a month, starting October 2. That means one day late counts as a full month of interest: $1,000 unpaid costs $7.50 for that month.
Your bill’s late payment schedule gives you the amount to pay for each payment date. Check it before paying, since the total depends on when your payment is made or mailed.
The short answer: 0.75% a month, starting October 2
For the second installment of tax year 2025, unpaid Cook County property taxes accrue interest at 0.75% per month starting October 2, 2026. The bill was due Thursday, October 1. State law sets the rate at 0.75% a month, or 9% a year, for these bills; the Illinois statute says interest applies for each month or portion thereof.
That wording means a payment one day late incurs a full month’s interest. If you owe $1,000, the first month costs $7.50. The amount grows while a balance remains unpaid, so use the late payment schedule printed on your bill to find the current total.
A payment sent through the U.S. Postal Service counts as on time if it carries an October 1 postmark or earlier. The interest rate was 1.5% a month, or 18% a year, before a 2023 law cut it in half for tax year 2023 and later.
Why the bills were due in October this year
The second-installment bills arrived about two months later than planned because of Cook County’s troubled property-tax computer overhaul. These bills usually come out in early July and are due in early August.
This year, the bills went online August 18 and were mailed by September 1, with about 1.8 million sent. The county announced the delayed release and October 1 deadline in its notice about the second-installment bills.
The recent schedule has shifted repeatedly: the second installment for 2024 taxes was due December 15, 2025, four months late; the first installment for 2025 taxes was due April 1, 2026, a month late; and this second installment was due October 1. You can check the Treasurer’s property-tax due-date information for the county’s posted dates.
How the late charge works, in plain terms
Cook County’s rate for tax year 2023 and later is 0.75% per month or portion of a month. The rate applies in counties with at least 3 million residents, which means Cook County. Interest starts the day after the due date printed on your bill.
Your bill includes a late payment schedule. Choose the amount that matches the date you mail or make your payment, instead of calculating the balance yourself. For a mailed payment, use the USPS postmark; a postage-meter date does not count as a postmark. FedEx and UPS payments count on the day they arrive.
Two exceptions apply. If your mortgage company held enough escrow to pay the bill and failed to send the payment, the interest is charged to the lender. Deployed National Guard and reserve members can receive a deferral. The state law on delinquent taxes sets out the applicable rules.
How to pay now, or pay over time
You can pay online for free at CookCountyTreasurer.com, at nearly 400 Chase branches, or at more than 100 Chicagoland community banks. Partial payments are accepted, so you can pay toward the balance without covering the full bill at once.
If you pay online while your bill is late, make only one payment per day. The Treasurer’s free Payment Plan Calculator, available since October 5, helps you set monthly or twice-monthly payments for a late balance over $100. Interest continues at 0.75% a month while you make payments.
Use the amount shown for your payment date on the bill’s late payment schedule. The Treasurer’s Payment Plan Calculator announcement explains the new option.
Before you pay: check for missing exemptions
Check your bill for the homeowner, senior, or senior freeze exemption before paying the full amount. If an exemption is missing, you can file a Certificate of Error with the Assessor for tax years back to 2021 and seek a refund.
The homeowner exemption is worth about $950 a year on average. The senior freeze has a household income limit of $65,000. If you qualify for an exemption that does not appear on your bill, contact the Assessor about filing the certificate.
If it stays unpaid: the tax sale, and the new law
Unpaid property taxes eventually go to the Annual Tax Sale, where investors buy the tax debt and can end up taking the property. The sale schedule is far behind: the next sale, expected in December 2026, covers unpaid tax year 2023 taxes after lawmakers delayed it in February 2026.
A law signed July 10, 2026, creates tax-deed auctions that return any leftover equity to the owner. It also ends private tax buying in Cook County after six more sales, which are expected to take place by 2030. Until a delinquent balance is resolved, interest can continue to increase what you owe, so check your bill’s payment schedule and available payment options.
Chicago vs. the suburbs, and the collar counties
Chicago and suburban Cook County homeowners pay the same Treasurer, follow the same due date, and face the same late-interest rate. The size of the bill increase differed: the median homeowner bill rose 3.2% in Chicago and 6.7% in the north and northwest suburbs.
DuPage County follows a different calendar and rate. Its 2025 property taxes were due June 1 and September 1, 2026, and late interest is 1.5% a month. The tax sale for unpaid 2025 taxes starts November 19, 2026.
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