Using your county's parcel search like an assessor would
Every Illinois county publishes a searchable roll. Most owners never open theirs.
Every Illinois county publishes a parcel search, and almost nobody uses it for what it is best at: looking at other people's properties. That is where a uniformity case comes from.
What is in there
For any parcel in the county, typically:
- Assessed value, split into land and improvement
- Prior years' assessed values
- Building characteristics — floor area, year built, storeys, rooms, basement, garage
- Lot size
- Class code
- Sales history
- Exemptions applied
- In some counties, the neighbourhood code the model uses
All of it public, for every property, at no cost.
The three searches worth running
1. Your own parcel, read properly
Not to see the assessment — you already know that from the notice — but to check every characteristic against reality. Floor area first, because it drives the model and it is the denominator of any uniformity comparison.
2. Your immediate neighbours
In Cook, PINs sharing your first three segments are on your block. Increment the parcel segment and walk along the street. This is the fastest route to genuinely comparable properties.
3. Your neighbourhood and class
Where the county allows searching by neighbourhood code and class — Cook does — this returns the model's own grouping. It is the closest you can get to seeing what the assessor sees.
Building the table
Open a spreadsheet and record, for each parcel you look at:
| Column | Where it comes from |
|---|---|
| PIN | Parcel page |
| Address | Parcel page |
| Class | Parcel page |
| Floor area | Characteristics section |
| Year built | Characteristics section |
| Improvement assessed value | Assessment section — not the total |
| $ per sq ft | You calculate: improvement ÷ floor area |
Ten or fifteen parcels takes half an hour. You will keep four to six of them.
The traps
Reading the total instead of the improvement. The most common error, and it invalidates every comparison.
Comparing across assessment years. Make sure every figure is from the same tax year. A parcel page may default to the most recent, while your notice is for the year under appeal.
Comparing post-exemption values. Some pages show taxable value after exemptions. That is not the assessment and it is not comparable across properties with different exemptions.
Trusting the floor area without checking your own. If your recorded area is wrong, your per-square-foot figure is wrong, and the entire comparison collapses — in whichever direction the error runs.
What to do with what you find
If your per-square-foot figure sits above a tight cluster of genuinely comparable neighbours, you have a uniformity argument, and the median of that cluster is the level you are requesting.
If your recorded characteristics do not match your building, you have something better: a factual error, which is not a matter of opinion and can often be fixed with a phone call rather than an appeal.