An Oak Park home that closes this fall carries two different tax numbers. One is printed on the listing. It comes from the 2025 bill that arrived in early September, which still rests on values set in the 2023 reassessment. The other comes from the 2026 reassessment notices that went out in May. The Oak Park Township Assessor puts the proposed combined increase across the village at 25%, and those values won't appear on a bill until summer 2027.
The two numbers meet first at the closing table. A seller's tax credit to the buyer is usually calculated from the older bill, and under the standard Chicago-area contract that credit is final once both sides sign.
The blank in Paragraph 12
Most residential deals in the Chicago area use the Multi-Board Residential Real Estate Contract 8.0. Paragraph 12 prorates general real estate taxes through the closing date. The proration is based on a percentage of "the most recent ascertainable full year tax bill," and the buyer and seller fill in that percentage themselves.
Illinois collects property taxes in arrears, so this credit matters. Say a seller closes in October 2026. The seller owned the home for most of 2026, but the 2026 tax bill won't be issued until 2027, and the buyer will pay it. The seller's credit at closing covers the seller's share of that future bill.
An explainer from the Chicago-area law firm Braverman & Makhlouf says 100% of the prior bill is common in years when assessments hold steady, and 105% to 110% is a negotiated cushion. In a reassessment year, the firm warns, 100% can leave the buyer under-credited because the old bill reflects the old assessment. The contract treats the proration as final at closing unless the parties agree otherwise in writing. When the 2026 bill arrives in 2027, neither side can reopen the number on its own. The same explainer describes other approaches the parties can choose: estimating with the new assessed value and the current tax rate, agreeing in writing to re-prorate later, or holding an escrow.
Oak Park closes 2026 inside its reassessment year, so every sale there this fall has an old bill on paper and a new assessment on record. What that new assessment means for one particular house is harder to read than the headline suggests.
Why the listing figure runs two steps behind
The tax figure on a listing this fall has moved through the following steps.
- 2023: The south and west suburbs, including Oak Park Township, were last reassessed.
- Early September 2026: Oak Park owners received second-installment bills for tax year 2025, still based on 2023-cycle values. Most bills rose about 3.9% from the year before, according to the Wednesday Journal's Sept. 29 Q&A. The increase came from a combined levy of $272 million, 3.2% higher than the year before.
- Oct. 1, 2026: Those bills came due. The year before, the due date was Dec. 15. Cook County blamed delays caused by its new property tax computer system. The normal target is Aug. 1.
- May 6, 2026: The Cook County Assessor released initial 2026 values for Oak Park Township. The Assessor's appeal deadline was June 18. The Board of Review window ran Aug. 3 through Sept. 1.
- 2027: The Assessor's office says values certified in 2026 affect second-installment bills issued in 2027.
The 3.9% rise on this fall's bills therefore reflects levies, not the reassessment. The Wednesday Journal Q&A says the May notices "have nothing to do with the bills that arrived in September."
Twenty-five percent describes the village as a whole
Township Assessor Ali ElSaffar has repeatedly said a 25% higher assessment does not mean a 25% higher tax bill. His office's 2026 reassessment explainer reduces the system to two parts. The first is the total levy that all local taxing bodies collect, $264 million in the year the explainer cites. The second is each property's share of the village's total assessed value. A property worth 1% of Oak Park's total assessed value pays 1% of the levy.
The comparison that matters is a single property's increase measured against the village's combined increase. A home that rises faster than Oak Park as a whole takes on a bigger share of the levy. A home that rises more slowly takes on a smaller share.
The 2026 notices show these shares moving by property type. The medians below were reported in the Wednesday Journal in May:
| Oak Park property type | Median assessed-value increase, 2026 initial notices |
|---|---|
| Townhomes | 11% |
| Commercial | 21% |
| Single-family homes | 24% |
| Condos | 25% |
| Apartment buildings | 28% |
Townhomes came in at less than half the village-wide figure. If those numbers survive appeals, the typical townhome's share of the levy shrinks, and the typical apartment building's share grows. A buyer looking at a townhome and a two-flat at similar prices this fall sees two prior-year bills on paper that will likely move in different directions in 2027.
The last reassessment shows how wide the spread can be. When bills based on the 2023 reassessment came out, about one-third of Oak Park homeowners saw their taxes go down, and about 40% had double-digit increases.
The village-wide 25% is also expected to fall. It is a proposed figure, and the Township says the combined increase will drop after appeals are decided. The explainer's illustration uses 20% as an assumed post-appeal figure, not a reported result. No final post-appeal total for Oak Park had been published as of early October. Even a property assessed at exactly 25% could still end up with a larger share once the village total settles.
The market behind the notices
The Township Assessor attributes the increase mainly to a stronger market since 2023. Oak Park's median home sale price was $513,000 at the 2023 reassessment and $595,000 at the 2026 reassessment. For single-family homes alone, the Cook County Assessor puts the 2025 median sale price at $596,000. Its median market-value estimate for the same class is $559,000.
Those figures give a buyer another point of comparison. The Township explainer lists three grounds for appeal. One is a recent purchase price or appraisal below the Assessor's market value. The others are comparable properties assessed for less and mistakes in recorded property characteristics, with overstated square footage named as the error most likely to lower an assessment. The Board of Review window for tax year 2026 closed Sept. 1. The next appeal period for Oak Park taxpayers is expected in the early months of 2027.
Riverside shows a gap within one township
Riverside Township makes the same point within a single assessment area. The Riverside-Brookfield Landmark reported average 2026 increases of 22% for single-family homes and 39% for condos. Land value increases ranged from 17.5% in the North Riverside part of the township to 75% in the Village of Riverside. Township Assessor Mary Jo Miller described the county's method as computer-based mass appraisal using several years of market data.
In the same township and the same reassessment, two homes can move very differently depending on how much of each home's value sits in the land.
Where the neighboring townships stand this fall
The other west-suburban townships are at different points in the same cycle, according to the Cook County Assessor's calendar:
- River Forest: Notices mailed April 20. Board of Review window was Aug. 3 to Sept. 1.
- Riverside: Notices mailed April 24. Board of Review window was Aug. 3 to Sept. 1.
- Berwyn: Notices mailed May 20. Board of Review window was Aug. 31 to Sept. 29.
- Lyons, which includes La Grange and Western Springs: Notices mailed July 23. The Assessor's deadline was Sept. 3. As of the Oct. 5 calendar update, Board of Review dates had not been posted.
- Proviso: Notices mailed Sept. 14. Assessor appeals are open through Oct. 27, 2026.
A Proviso sale closing this month could close while the property's 2026 value is still open to appeal. An Oak Park sale closing this month has a 2026 value that is past both review windows but not yet on a bill.
A few practical questions
Will the seller's exemptions carry over to me? No. Exemptions apply to an owner, not to the property. The Wednesday Journal reports that the Homeowner Exemption lowered most Oak Park bills by $1,166 this year. It renews automatically for most taxpayers, but new owners have to apply. The Oak Park Township Assessor's office at 708-383-8005 helps with exemption questions.
Where can I see a specific property's 2026 value? The Cook County Assessor publishes township valuation reports and parcel-level assessed values. Current-year values can still change through Assessor and Board of Review review.
When does Oak Park's next reassessment notice come? Cook County reassesses one-third of the county each year. The south and west suburbs come up again three years after this cycle.
If you're buying or selling in Oak Park, River Forest or Riverside this fall, The Chris Demos Group can go over the 2026 assessment on a specific property and show you how the proration on your contract is figured, alongside your attorney, before you sign. Call Chris.
This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.
