Quadrennial reassessment: the year your number actually gets rebuilt
Most of Illinois reassesses every four years. Cook works on a three-year triad. Knowing your year changes your timing.
Illinois counties reassess on a cycle. Cook County works on a triennial pattern — every township is reassessed once every three years — while most other Illinois counties operate a quadrennial cycle, reassessing every four years.
Knowing which year you are in changes both what happened to your number and what argument is available to you.
What happens in a reassessment year
Your value is rebuilt from scratch. The assessor's model is re-run against recent sales, and your property gets a new value reflecting what the market has done since the last cycle. In a rising market this is where the large increases appear — often the entire market movement of three or four years arriving in one notice.
That concentration is why reassessment years generate the most appeals and the most alarm. A 30% increase in one year sounds outrageous; spread across the four years it actually represents, it may be an ordinary market.
What happens in the other years
Between reassessments your value normally stays put, other than for:
- New construction or demolition — an addition, a finished basement, a torn-down garage.
- A change of use or class — a property converted from residential to commercial.
- Corrections, including ones you obtained by appealing.
- The equalisation factor, which can move your equalised value with your assessed value unchanged.
Why the cycle matters to your argument
In a reassessment year the new value is fresh and the evidence behind it is recent. A market-value argument has to contend with sales the assessor has just examined. But this is also the year the most new errors are introduced, because every parcel was re-valued at once — so the record itself is worth checking closely.
In an off year your value is carried forward. If the market has fallen since the reassessment, your assessment reflects a market that no longer exists, and that is a genuine argument. Illinois allows appeals in every year, not only reassessment years, and this is the situation people most often fail to notice.
The uniformity argument does not care about the cycle
Worth emphasising, because it is the ground most owners overlook. A uniformity claim compares your assessment per square foot against comparable properties assessed in the same cycle, by the same model. If the model treated you differently from a near-identical neighbour, that inconsistency is present in a reassessment year and every year after it, until the next reassessment resets everything.
This is also why a successful uniformity appeal is worth more than one year's saving. The correction generally holds for the remainder of the cycle, so a win early in a three-year Cook cycle is worth roughly three times its annual value.
Finding your year
Cook County publishes its triennial schedule by township — the city, the north suburbs and the south suburbs each take a turn. Other Illinois counties publish a quadrennial schedule through the Supervisor of Assessments.
Two dates to note. Your reassessment year tells you when the number was rebuilt. Your appeal deadline is a separate date, usually 30 days from publication of your township's assessment roll, and it is not negotiable — a late filing ends the appeal outright with no cure. Check it with your county rather than relying on last year's date.