What the county's own roll says, and how many parcels sit above their neighbours.
1,878,782parcels on record
1,766,472with a published assessment
$27,000median assessed value
373,305above their neighbourhood median
Among those, the typical excess is $13,198 of
assessed value above the median for like-classified land in the same town — $4,926,951,677
in total across Cook County.
A median has half of everything above it by definition, boards do not grant every
uniformity claim, and being above a median is a ground to argue rather than proof of error. These
are assessed values, not tax bills.
Your deadline in Cook County
30 days from the publication of your TOWNSHIP's assessment roll. Cook reassesses on a rolling three-year, township-by-township calendar, so your window depends on your township and not on the county.
Statutory basis: 35 ILCS 200/16-55.
A late filing cannot be cured, so confirm the date on your own notice — it is not the same across the county.
How the assessment was calculated
Illinois assesses at 10% of market value, except in Cook County, which uses its own classification ordinance with residential property at 10%.
The assessor estimates market value by mass appraisal — a model over recent sales, adjusted by the
characteristics they hold on file for your property. If those characteristics are wrong, the number
is wrong. The full anatomy is here.
The argument most people miss
Beyond “my house is worth less than they say”, the Illinois Constitution requires uniform
taxation. If comparable property near you is assessed at a lower rate per square foot, that is a
ground for relief in its own right — no appraisal needed, and built from figures the assessor
published themselves.