March 25, 2026
If you own property in Cook County, your window to appeal your assessment does not stay open all year. Each township has its own filing period, set by the Assessor and revised through the year, and missing it means waiting for the next one.
This guide explains how that calendar works. It deliberately does not list dates. An article is a fixed document that stays online long after it is written, and a deadline is the one fact on the page a homeowner would act on — which makes a published date in an article the single most dangerous thing on it. The county's calendar is the authority, and it is linked in every section below.
Cook County reassesses on a triennial (3-year) cycle, divided into three districts: the south and west suburbs, the north suburbs, and the City of Chicago. Each district is reassessed in a different year of the cycle, and each township within a district opens on its own schedule.
Two things follow from that, and they are the two most common misunderstandings:
Your neighbour's deadline is probably not your deadline. Townships in the same district open weeks apart, and Chicago neighbourhoods can span more than one assessment township. Your township is determined by the county's own record for your PIN, not by which neighbourhood or suburb your address is described as being in.
Being outside your reassessment year does not mean you cannot appeal. You can appeal your existing assessment in the years between reassessments too. The reassessment year is simply when the Assessor is actively re-deriving values, which is when a well-evidenced appeal has the most to work with.
There is exactly one reliable route, and it takes a few minutes:
Our own township deadline pages show a filing window only where we have verified it against that calendar and can show you when we read it. Where we have not, they show no date and say so. That is deliberate: a date we cannot attribute is not a date worth planning around.
Verify your assessed value. It is on your most recent tax bill and in the Assessor's record for your PIN.
Check for over-assessment. A residential assessment is set at 10% of the Assessor's estimate of market value. If comparable properties are assessed materially lower than yours, that gap is the argument.
Gather comparable evidence. The strongest first-level appeal argument is comparable assessments and relevant recent sales for properties genuinely similar to yours — same class, similar size, similar age, nearby. This is what Rule 15 evidence refers to.
File before the last file date for your township. Not the county's "typical" window, and not the date on a blog post. Yours.
The Board of Review is a separate, later stage with its own calendar, and it is frequently confused with the Assessor's window. If you have missed the Assessor's window, the Board is a real and separate opportunity, and it is worth looking into at cookcountyboardofreview.com.
OverTaxed IL does not file, sign, prepare, handle, or represent anyone at the Cook County Board of Review. Under the Board's own rules, only a licensed attorney or the taxpayer personally may practise before it. If we ever offer anything at that stage, it would be attorney-led. Do not wait for us — confirm your own deadline with the county.
OverTaxed IL analyzes public Cook County records and prepares a defined Assessor-stage appeal packet. You review it, sign it, and file it yourself.
Run a free check on your property and we will pull your current assessment from the public record and compare it against comparable properties.
This free check compares available public Cook County records. It estimates whether the evidence appears to support closer review. It does not predict whether an appeal will succeed or reduce taxes.
The $69 packet is a preparation service. We prepare it; you review it, sign it, and file it with the county yourself.
OverTaxed IL is not a law firm and does not provide legal or tax advice. We do not guarantee a reduction. County decisions are final, and a change in assessed value does not produce an equal change in a tax bill. You can file on your own with the county at no cost.