The 2026 Cook County Reassessment and What It Does to Your Assessed Value

What a reassessment year actually changes

Cook County reassesses property on a triennial cycle, which means one third of the county gets a fresh estimated market value every year and each parcel comes up once every three years. For 2026, the section in the chair is the south and west suburbs, the same triad that was last reassessed in 2023. This is not a tax bill and it is not a rate change. It is the Assessor's Office resetting the number that everything downstream is built on: your estimated fair market value, and from that your assessed value.

The mechanics are worth getting right because owners constantly confuse them. For residential property in Cook County, the assessed value is roughly 10 percent of the estimated market value the Assessor assigns. For most commercial and industrial property it is about 25 percent. A reassessment moves that estimated market value based on sales of similar properties over the prior three years, and the new figure then runs through the state equalizer, local rates, and your exemptions before it becomes a dollar amount you owe. If you want the full walk from valuation to bill, our Cook County Assessor's Office guide lays out each step.

Here is the timing that trips people up. Values certified in 2026 do not show up on a bill until the Second Installment that issues in 2027. That lag is exactly why the reassessment notice you get this spring or summer is the moment to act, not the bill you open next year. By the time the higher number lands in your mailbox as a payment, the cheap, owner driven window to challenge it has closed.

Which townships are reassessed in 2026

The 2026 reassessment covers the suburban townships south of North Avenue, outside the City of Chicago. These are the same communities that carried the brunt of the last cycle, and they are being revalued again now. The Assessor mails reassessment notices township by township on a rolling schedule that starts in the spring and runs through the summer, so there is no single countywide date. Each notice carries its own appeal deadline printed on the page.

If your township is on this list, your estimated market value is being reset this year. The official, parcel level dates live on the Assessor's assessment and appeal calendar, which updates as each township opens and closes.

• Berwyn (notice mailed May 21, 2026, appeals due July 6, 2026)
• Palos (appeals due July 17, 2026)
• Cicero (appeals due July 31, 2026)
• Riverside, River Forest, and Oak Park (windows opened and closed earlier in 2026)
• Stickney, Lyons, Bremen, Lemont, Worth, Calumet, Proviso, Orland, Thornton, Rich, and Bloom (rolling through the summer)

How assessed values are actually moving

The honest answer is that it varies block by block, because the Assessor is chasing recent sales, not applying a flat percentage. The early 2026 township releases give a useful read. In Berwyn, the Assessor reported a 2025 median single family sale price of $328,000 against a median market value estimate of $300,000 for that same class, which is the office signaling it is coming in a bit under recent sales rather than ahead of them. That is a deliberate posture from Assessor Fritz Kaegi's office, which has spent the cycle stressing that an assessment increase does not translate one for one into a tax increase.

But the 2023 cycle is the cautionary tale sitting right behind this one, and these are the same townships. In that reassessment, total assessed value across the south and west suburbs jumped 27.4 percent, and the median homeowner in the south and southwest suburbs ended up with a property tax bill that rose nearly 20 percent, the largest percentage increase in at least 30 years. Those increases did not land evenly. Working class neighborhoods absorbed some of the steepest jumps while the countywide picture looked more moderate.

It also matters that residential and commercial parcels are valued by completely different machinery. A home is valued off recent sales of comparable houses, which is intuitive and easy to challenge with a few neighboring sales. Commercial property is valued off its use, estimated income, market level vacancy, collections loss, and operating expenses, an income approach that is far more contestable and that gives well represented owners a lot of room to argue the number down. That asymmetry is a big part of why commercial appeals so reliably succeed while many homeowners never file, and it is the structural reason the burden tends to drift toward houses.

The lesson is not that 2026 will repeat 2023 to the decimal. It is that a reassessment in this part of the county has a documented history of moving real money, and the owners who came out worst were disproportionately the ones who did nothing when their notice arrived. Treating the estimated market value on your notice as a starting offer rather than a verdict is the entire game.

The burden shift hiding inside the appeals data

There is a structural quirk in Cook County that homeowners rarely hear about until it has already cost them, and the Assessor's own data from the 2023 cycle spells it out. Going into that reassessment, residential property made up 68 percent of total assessed value in the south and west suburbs and non residential made up 32 percent. After the Assessor set values, the residential share actually ticked down slightly, to 67 percent, meaning the office had nudged a sliver of the burden toward commercial.

Then the appeals happened. After the Board of Review processed challenges, the residential share climbed to 71 percent and non residential fell to 29 percent. The Assessor's office reported that non residential assessed value dropped roughly $950 million, just over 18 percent, during the Board of Review stage. In plain terms, commercial and industrial owners appealed aggressively and won real reductions, and because property tax is a fixed pie divided among everyone, every dollar knocked off a commercial parcel quietly reslid onto homeowners. You can see why the Assessor flagged this as a burden shift.

The takeaway for a 2026 homeowner is blunt. Commercial owners treat the appeal process as routine cost control. If you sit out your own appeal while they file theirs, you are not staying neutral, you are volunteering to carry the share they shed. The system rewards the people who show up.

The appeal windows: Assessor first, then Board of Review

Cook County gives you two separate bites at the apple, and they are sequential offices with separate deadlines, not one process. The first is the Cook County Assessor's Office. When your township's reassessment notice mails, the appeal window opens for roughly 30 days, with the exact close date printed on the notice. This is the cheapest, fastest stage. You can file online in about twenty minutes, and the office tells owners that if the property characteristics are correct and the estimated market value is within 10 percent of what the home would realistically sell for, an appeal probably will not move the needle. If it is off by more than that, or the characteristics are wrong, you file.

The second stage is the Cook County Board of Review, a separate elected body of three commissioners that opens its own appeal window for each township after the Assessor's window closes. You do not need to have appealed at the Assessor level to appeal at the Board, and plenty of owners who got a partial reduction from the Assessor go to the Board to push for more. Beyond the Board sits the state Property Tax Appeal Board, or PTAB, for owners who want to escalate further. For the difference between fighting your assessment and simply moving on, our piece on appealing your assessment versus selling your home is worth a read before you commit to a year of paperwork.

The evidence that wins at both levels is the same: recent sales of comparable properties, and lack of uniformity, meaning similar homes near you carrying lower assessments. You are not arguing that taxes are too high, which no one at these offices can fix. You are arguing that your specific number is wrong relative to the market and relative to your neighbors.

How to read your own notice and find your number

When the envelope arrives, do three things before you decide anything. First, check the property characteristics, square footage, number of bedrooms and baths, lot size, because a clerical error inflating your home is the easiest appeal to win. Second, look at the estimated market value and ask honestly whether your house would sell for that today. Third, note the appeal deadline, because once it passes for your township you are waiting until the next stage or the next year.

If you are not sure what your parcel currently carries or where to confirm the new figure, start by pulling your record. Our guide to looking up your property tax bill in any Illinois county shows exactly where the assessed value, exemptions, and history appear, so you can compare the old number to the reassessment notice side by side. Confirm your exemptions while you are in there, because a missing Homeowner or Senior Exemption costs you more than most appeals would ever recover.

It also pays to gather your comparables now, while the market is fresh, rather than scrambling the week your deadline lands. Pull three to five recent sales of homes genuinely like yours, same township, similar size, age, and condition, and note any nearby homes carrying lower assessments than yours despite being comparable. That second category, lack of uniformity, is often the stronger argument, because it shows your number is out of line with your own neighbors rather than just high in the abstract. The Assessor and the Board both respond to that kind of concrete, parcel level evidence far more than to a general complaint that taxes feel too high.

One more discipline point: do not let the rolling notice schedule lull you. Because townships mail on a staggered basis, your neighbor two suburbs over may already be past their deadline while yours has not opened. That staggering is normal, but it means general news about the reassessment being underway is not a substitute for watching your own township's specific date on the Assessor's calendar.

The read for owners and sellers

If you intend to stay, the reassessment is a chore you should not skip. File your Assessor appeal inside the window, go to the Board of Review if the first answer is thin, and lock in every exemption. The owners who do this routinely are the reason the burden keeps sliding toward the owners who do not. In a triennial county, the number you accept in 2026 follows you for three years, so a successful appeal is not a one time refund, it is three cycles of a lower base.

If you are weighing a sale, the calculus is different and the timing is unusually clean. A higher reassessment can dent buyer demand and stretch days on market, because a sophisticated buyer prices the future tax bill into their offer. Selling before the 2027 bill reflects the new value lets you hand that uncertainty to the next owner rather than absorbing it. For owners who do not want to spend a year appealing or pour money into repairs while the tax base resets under them, an as is cash sale is the cleaner exit. See how that works for sellers on our sellers page, and if the numbers matter more than the timeline, you can get a cash offer and compare it against the cost of holding through the reassessment.

Either way, the worst move is the passive one. The reassessment is happening to your parcel whether you engage or not. The only question is whether you are the owner who shapes the number or the one who inherits it.