What to Know About Cook County Property Tax Proration in 2026

A seller in Logan Square pulls up her closing disclosure two days before settlement and finds a line she wasn't expecting to question: a property tax credit for just over nine thousand dollars, coming straight out of her proceeds. She calls her attorney. The math checks out against last year's bill. What she doesn't ask, because she has no reason to know to ask it, is whether "last year's bill" is still a number worth trusting this particular fall.

That question matters more in 2026 than it has in years. Two separate Cook County problems are landing on the same closing table at the same time, and neither one shows up on the standard proration worksheet every title company hands you.

The Formula Everyone Quotes

Illinois property taxes are billed in arrears. That timing is why property-tax proration matters at closing: a tax bill can cover months when the seller owned the home.

Cook County splits that annual bill into two installments. According to Younis Law Group, the first is fixed by law at 55 percent of the prior year's total tax, so it tells you almost nothing about current value. The second installment is the one that actually reflects the new tax rate, the new equalization factor, and any exemption changes, which is why it's the number everyone waits for.

Since nobody has that final number in hand at closing, title companies estimate. Vesta Preferred describes the common convention as taking the most recent full year's bill and multiplying it by something between 100 and 120 percent. That provides a buffer against the increase that's probably coming. That percentage shapes the estimate.

In a normal year, that's a reasonable guess. This isn't a normal year.

Two Things Stacking on the Same Bill Cycle

According to WTTW, Cook County Board President Toni Preckwinkle announced on June 9, 2026, that the second installment of 2025 property tax bills, normally mailed in early July and due in early August, will be about two months late, pushing payment to at least October. She did not commit to a firm mailing date or a firm due date.

This is not a one-year hiccup. The first installment of 2025 taxes was already a month late, coming due April 1 instead of the usual March date. According to Cook County, the second installment of the tax year before that, 2024, was delayed even further: it didn't mail until November 14, 2025, with payment due December 15, 2025, a delay of roughly four months. When those bills finally arrived, the countywide average increase was 16 percent, and some West and South Side neighborhoods saw increases topping 100 percent. Buyers and sellers who had used a proration estimate that fall found out only after closing how far off that estimate had been.

Chicago Public Schools alone took on an extra $33 million in borrowing costs because of the 2024 delay, since the district budgets around when that revenue is supposed to land. That's the scale of disruption a late bill creates even for institutions with financial staff whose full job is tracking this. A homeowner closing on a three-flat has far less room to absorb the same kind of miss.

Lower My Taxes notes that 2026 is the triennial reassessment year for Cook County's south and southwest townships, including Berwyn, Palos, and Cicero, each with its own filing deadline in July. Properties in a reassessment year can see assessed values shift substantially, which means the bill built on the new value can differ from the prior year's bill by a wide margin, in either direction. If you're closing on a home in one of those townships this fall, your proration estimate is built on a bill from before the reassessment even happened.

Here's how the timeline actually lines up for anyone closing between now and the end of the year:

So the most complete, most recent full-year tax bill available to base a fall 2026 closing on is the tax year 2024 bill, a bill that was itself unusually late and reflected an unusually large jump. That's the foundation the standard proration percentage is being built on right now.

The delay itself doesn't cost you a dollar. Not knowing it's there when you sign the proration language in your contract might.

What This Means If You're Selling This Fall

If you're listing a Chicago-area home right now, the proration credit at closing isn't a minor line item to skim past. It comes directly out of your net proceeds, and the percentage your contract uses determines how much.

A few things worth confirming with your attorney before you're staring at the closing disclosure with a pen in hand:

• Which specific percentage does your contract use for the proration multiplier, and is it written as a flat number or tied to an actual current assessment
• Is your property in one of the 2026 reassessment townships, and if so, has your attorney priced the estimate off the old assessed value or a newer one
• Does the contract include a re-proration clause that lets both sides true up the number once the actual second-installment bill for 2025 finally arrives, as Lysinski explains?
• Have you confirmed any exemptions on file are current?

What matters is whether the number is close to right or built on a bill the county itself is still catching up on.

What This Means If You're Buying This Fall

Buyers have the opposite exposure. You're the one who eventually receives the actual full-year bill, whenever the county gets around to sending it, and the final amount may not match the seller's credit.

Because the second-installment bill for 2025 hasn't shipped as of mid-August, and the county isn't promising a firm date, you're closing this fall without the one document that would tell you the real number. A re-proration agreement, where both sides agree to true up once the actual bill posts, is the practical way to protect against a credit that turns out to be too light.

If the property sits in Berwyn, Cicero, Palos, or another township going through the 2026 reassessment, ask specifically whether the proration was calculated off the old assessed value or an estimate that accounts for the pending reassessment. The difference between those two approaches, in a reassessment year, is exactly where sellers and buyers have historically ended up surprised on opposite sides of the same number.

A Note for Anyone Moving In From Out of State

If you're relocating from a market where property taxes are billed and paid within the same year you owe them, the Illinois arrears system takes some getting used to on its own, before you add the recent Cook County billing delays. This is the kind of detail that matters more when you're managing a move that also involves a home in Wisconsin, where the billing calendar works differently. Knowing which system applies to which closing, and when, is part of what makes a cross-state move manageable instead of confusing.

A Few Questions We Hear Often

How does a delay affect the closing credit? It affects how accurate the credit turns out to be.

What if my property isn't in one of the 2026 reassessment townships? The reassessment risk is smaller for you, but the billing delay still applies countywide. Every Cook County closing this fall is working from the same incomplete data trail on the second installment.

Will next year's bills be back on a normal schedule? The Evanston RoundTable reports that county officials expect this year's delay to be shorter than 2025's four-month slip, and there's a reasonable chance next year's cycle returns closer to normal. Nothing about that is guaranteed given the recent delays, so it's worth treating each closing on its own terms rather than assuming the schedule has stabilized.

Cook County has had repeated tax-bill delays, and there's no way to fix those from a closing table in Logan Square or anywhere else in the city. What you can control is whether the number on your statement reflects an educated estimate or a guess nobody checked twice.

If you're weighing a fall closing in Chicago, or coordinating one alongside a move to or from Wisconsin, the Phair-Hinton Group works through exactly this kind of timing detail before it becomes a surprise at the table. Let's get you home, schedule a call to get started.

This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.