When Does Cook County Reassess Property Taxes? The Triennial Cycle Explained

If you're wondering when does Cook County reassess property taxes, the answer is every three years — but not all at once. Cook County uses a triennial reassessment cycle that divides the county's 30+ townships into three groups called triads. Each triad is reassessed on a rotating three-year schedule, meaning roughly one-third of the county gets new assessed values each year.

Understanding this cycle is critical for property owners because reassessment years are when the biggest changes to your tax bill happen. Here's everything you need to know about when your property will be reassessed and what that means for your taxes.

The Three Triads: How Cook County Divides Reassessments

Cook County splits its townships into three triads based on geography. Each triad is reassessed once every three years, and the cycle repeats indefinitely. The current schedule is:

Triad	Most Recent	Next Reassessment	Following
North/Northwest Suburbs	2024	2027	2030
City of Chicago	2025	2028	2031
South/Southwest Suburbs	2026 (current)	2029	2032

Right now in 2026, the south and southwest suburban triad is being reassessed. If you own property in a south or west suburban township, your assessed value is being updated this year.

Every Township and Its Triad

Not sure which triad your property falls in? Here is the complete list of Cook County townships organized by triad.

City of Chicago Triad (2025, 2028, 2031)

Hyde Park, Jefferson, Lake, Lake View, North Chicago, Norwood Park, Rogers Park, South Chicago, West Chicago

North/Northwest Suburban Triad (2024, 2027, 2030)

Barrington, Elk Grove, Evanston, Hanover, Leyden, Maine, New Trier, Niles, Northfield, Palatine, Schaumburg, Wheeling

South/Southwest Suburban Triad (2026, 2029, 2032)

Berwyn, Bloom, Bremen, Calumet, Cicero, Lemont, Lyons, Oak Park, Orland, Palos, Proviso, Rich, River Forest, Riverside, Stickney, Thornton, Worth

What Happens During a Reassessment Year

In a reassessment year, the Cook County Assessor's Office reviews and updates the estimated fair market value for every property in the affected triad. This involves analyzing recent sales data, income and expense information for commercial properties, and current market conditions. The Assessor then publishes new proposed assessed values, and property owners receive reassessment notices in the mail.

This is when the largest assessment changes occur. It's not unusual for commercial property assessments to jump 20%, 30%, or even more during a reassessment year — especially if the local real estate market has changed significantly over the prior three years.

The reassessment also sets your base assessed value for the next three years. While the equalization factor and tax rates change annually, your underlying assessed value stays the same until the next triennial reassessment (unless you successfully appeal).

What Happens in Non-Reassessment Years

In the two years between reassessments, your property's assessed value generally stays the same. The Assessor does not review or update individual property values. However, your tax bill can still change because tax rates and the equalization factor are recalculated every year.

This means your property tax bill can go up even in a non-reassessment year if taxing districts increase their levies or if the equalization factor rises.

Can You Appeal in a Non-Reassessment Year?

Yes. This is one of the most common misconceptions about Cook County property taxes. You can file an appeal with the Assessor's Office every year, regardless of whether your triad is being reassessed. You can also appeal to the Board of Review every year.

That said, reassessment years offer the best opportunity for significant reductions because the Assessor is actively recalculating values. Appeals during non-reassessment years tend to result in smaller adjustments, but they are still worth filing if your property is over-assessed.

Why Reassessment Years Matter Most

The reassessment year is the single most important year in the property tax cycle for three reasons:

1. Biggest assessment changes happen here. The Assessor is updating values based on current market data, which means assessments can move substantially — up or down.

2. It sets your base for three years. Whatever assessed value you end up with after the reassessment (and any appeal) becomes your baseline for the next three years. Getting a reduction in the reassessment year saves you money for three consecutive tax bills.

3. Appeal deadlines are tied to the reassessment schedule. When your triad is reassessed, the Assessor publishes township-specific filing deadlines. Miss your window, and you lose your best shot at a reduction.

How to Find Out When Your Property Is Next Reassessed

The simplest way is to look up your township in the lists above and check which triad it belongs to. You can also visit the Cook County Assessor's website and search for your property by PIN (Property Index Number) — your property record will show which triad and township you're in.

If your property is in the south/southwest suburban triad, your reassessment is happening right now in 2026. If you're in the north/northwest suburbs, your next reassessment is 2027. City of Chicago properties were reassessed in 2025 and won't be reassessed again until 2028.

How TaxRival Can Help

Whether your property is in a reassessment year or not, TaxRival can analyze your assessment and determine if you're overpaying. We handle the entire appeal process — from pulling comparable sales and income data to filing with the Assessor and Board of Review — at a 25% contingency fee, which is well below the industry standard of 30-50%. If we don't reduce your assessment, you pay nothing.