Cook County's triennial reassessment and the three triads
Your township is reassessed every third year. Knowing which year is yours changes when to act.
Cook County is divided into three assessment districts — commonly called triads — and reassesses one each year, so every property is reassessed on a three-year rotation.
The triads
The City triad covers Chicago. The North and South triads cover the suburban townships. The Assessor publishes which is being reassessed in a given year, township by township, with the schedule available in advance.
Why your year matters
In your reassessment year the value is rebuilt and the largest changes — and the largest new errors — appear. It is also the year with the most attention available to correct something.
Between reassessments
Values generally hold, moving for equalization, permitted improvements, or an individual appeal outcome. You may still appeal in an off year: the right is annual, and a uniformity argument does not depend on your value having just changed.
Timing your filing
Appeal windows in Cook open township by township as reassessment notices go out, and each township's window is short. Watch for your township's opening rather than waiting for a single county-wide date — there is not one.