The Tax Number on a La Grange Contract Runs a Full Reassessment Behind

If you buy or sell a La Grange home between now and late 2027, your taxes will be settled using a bill from before Lyons Township's 2026 reassessment. That bill was based on the township's 2023 values. Under the standard Illinois residential contract, the ordinary tax proration on an existing home is final once the deal closes, unless the parties agree otherwise in writing. The form makes a separate exception for an improved property that hasn't yet been taxed for a full year as currently improved. In practice, that means buyers and sellers negotiate the effect of the reassessment when they fill in a single percentage on the contract, well before any new bill shows up.

The rest of this post covers how that gap opened, how big it might be, and where it appears in the paperwork.

Two Clocks on One Tax Bill

Cook County reassesses one-third of the county every year. The Cook County Assessor's Office says the south and west suburbs, Lyons Township included, were last reassessed in 2023. Lyons Township covers all or part of La Grange, Western Springs, Countryside, Indian Head Park, Burr Ridge, Willow Springs, Brookfield and several other villages.

Here is the 2026 timeline in order:

1. July 23, 2026. The Assessor mailed reassessment notices to Lyons Township homeowners.
2. September 3, 2026. The deadline to appeal to the Assessor passed.
3. October 1, 2026. Second-installment bills for tax year 2025 were due. Those bills still reflect the earlier assessment cycle.
4. October 8, 2026. The Cook County Board of Review opened second-level appeals for Lyons Township.
5. November 6, 2026. The Board of Review filing window for Lyons closes, and evidence is due November 16.
6. 2027. The Assessor says values certified in 2026 "will affect second-installment tax bills issued in 2027."

Even the first installment in 2027 won't show the new values. The Cook County Treasurer explains that the first installment is 55% of the previous year's total tax, and exemptions are applied on the second installment. So the reassessment only reaches a La Grange homeowner's actual bill on the second installment of tax year 2026, issued in 2027. Until then, every tax figure on a listing sheet or a closing statement comes from the old cycle.

How Far the Values Moved

The Assessor's Lyons Township residential valuation report puts the 2026 median estimated market value for single-family homes at $418,000. The 2025 median sale price was $462,000. In the 2023 cycle, the Assessor's median estimate for single-family homes was $346,000. Going from $346,000 to $418,000 is an increase of roughly 21% in the median estimate between cycles.

The estimate sits below what homes actually sold for in 2025 because, as Assessor Fritz Kaegi put it in the office's Lyons Township release, "assessments in Cook County reflect market value over the last three years."

Independent analyses of individual parcels point to a similar range. A Cook County tax appeal firm's analysis found a median 25.1% increase from 2025 final values to 2026 notice values across 38,177 homes, with 96.9% of those homes going up. A separate open-data analysis calculated a 24.4% median increase among 30,233 houses that had values in both years. Both numbers are preliminary. The county's own assessed values dataset notes that current-year values can still change until the Board of Review certifies them.

Neither the Assessor nor anyone else has published a median change for La Grange alone. Your PIN's notice is the only number that applies to your house.

Why a 25% Assessment Increase Doesn't Become a 25% Tax Increase

On its assessment and tax bill page, the Assessor answers the question of whether a higher assessment means a higher bill with "Not necessarily." The page names the levies set by local taxing bodies as a key factor, alongside your assessment and your exemptions.

The Cook County Clerk describes how the system works. Each district asks for a dollar amount. The Clerk then sets the rate needed to raise that amount across the total taxable value. If the levy stays the same and the base gets bigger, the rate goes down. Separately, the Illinois Property Tax Extension Limitation Law caps how much a covered district's levy on existing property can grow, generally at the lesser of 5% or CPI. New construction and voter-approved increases are added on top. The Illinois Department of Revenue is clear that this law limits district revenue and does not "cap" individual bills or assessments. The state equalization factor, 3.0300 for Cook County in tax year 2025, is applied on top of assessed values.

Put together, your bill depends less on how much your value rose than on how much it rose compared with everyone else in your taxing districts.

The North Suburbs Went Through This in 2025

Cook County's north and northwest suburbs were reassessed for tax year 2025, and the Clerk's 2025 Tax Rate Report, published September 23, 2026, shows what happened next.

In the reassessed region, average values rose by nearly a quarter and the average rate fell by about an eighth. The average bill still rose by about a tenth. That is regional data, and the Clerk notes that individual bills vary. It's still the most recent Cook County example of a value jump close to what the independent analyses found in Lyons.

The south suburbs' own last cycle tells a similar story. After the 2023 reassessment, the Cook County Treasurer's tax year 2023 bill analysis reported that the median bill for south and southwest suburban homeowners on tax year 2023 bills, billed in 2024, rose 19.9% to $6,117. That figure covers the whole region, not Lyons Township alone.

What Goes Into a La Grange Bill

Even without a reassessment, La Grange rates have been going up. The Clerk's report puts the Village of La Grange's average composite rate for tax year 2025 at 8.797545 per $100 of taxable value, up 4.92% from 8.385012 in 2024. That composite is an average across the village. Your own rate depends on which districts serve your PIN, and La Grange addresses can fall in School District 102, 105 or 106.

School districts make up most of the rate. When those levies are spread over a bigger 2026 assessed base, their rates should fall in the way the Clerk describes. The levies themselves are set by each board, though, and none of them has published what it plans to levy for tax year 2026.

Where the Gap Shows Up in the Contract

Paragraph 12 of the Multi-Board Residential Real Estate Contract 8.0 says general real estate taxes are prorated through the closing date "based on ___% of the most recent ascertainable full year tax bill." It also says "all general real estate tax prorations shall be final as of Closing," except under subparagraph b), which covers improved property that hasn't been taxed for a full year as currently improved, or "as otherwise agreed by the Parties in writing." The form was approved in February 2025 by the Chicago Bar Association and other participating organizations.

Illinois taxes are paid in arrears. The Illinois Department of Revenue explains that on an existing home, the seller generally gives the buyer a credit for the time the seller owned it, and the buyer pays the bills that come due after closing, subject to the contract. For a La Grange closing in the coming months, the "most recent ascertainable full year tax bill" is the tax year 2025 bill, which predates the reassessment. The seller's credit for 2026 is calculated from that older bill. The buyer then pays the 2027 second installment, which is the first one to reflect the new values.

That makes the blank percentage the only place the contract deals with the reassessment. Illinois real estate attorney Lauren Jackson writes that 105% to 110% is typical in her practice. Younis Law Group describes methods at 100% and 105% and says the percentage is negotiable. Each five points is a real dollar amount on a La Grange bill. The 2026 notice value, the 2023 value and the north suburbs' 2025 numbers are all public, and all of them exist before the percentage gets filled in. The same paragraph also asks a seller to preserve any exemptions reflected in the bill being used.

This post is general information, not legal, tax or financial advice. Your attorney and the PIN-level records for your property are the right sources for your own transaction.

The Window Still Open This Week

The Board of Review accepts Lyons Township filings through November 6, and filing is free. Over the summer, Southwest Regional Publishing reported that Lyons Township Assessor Pat Hynes and staff were holding after-hours reassessment help sessions around the township, including one at La Grange Village Hall on August 17. For a home that's listed or under contract, whatever the Board of Review decides by its certification becomes the value on the first bill the buyer pays in full.

Quick Answers

Does the tax figure on a La Grange listing reflect the 2026 reassessment? No. Listings generally show the most recent bill, which is tax year 2025, and the new values first appear on second-installment bills issued in 2027.

Will my taxes go up as much as my assessment did? Probably not. The Assessor's answer is "not necessarily." Rates adjust to the size of the base, and in the north suburbs' 2025 reassessment, average values rose 24.37% while average bills rose 10.24%.

Can a proration be corrected after closing once the 2027 bill comes out? Under paragraph 12(a) of the 8.0 contract, ordinary tax prorations are final at closing unless the parties agree otherwise in writing.

If you're pricing a La Grange home or weighing an offer this fall, I'm happy to sit down with your 2026 notice, recent Lyons Township sales and your attorney's input so the pricing conversation starts with the full tax picture. Let's connect. Start with a free home valuation from Jeff / Amjad Salhani & Associates, and see our La Grange neighborhood guide for a wider look at the village.