Your PIN, and how to read it
The property index number encodes where your parcel sits. It is also the only identifier that is never ambiguous.
Every Illinois parcel has a Property Index Number — the PIN, sometimes called a parcel number or permanent index number. It is usually ten or fourteen digits, printed with dashes.
It encodes location
The segments generally run township, section, block, parcel and sometimes unit. Two parcels with PINs differing only in the last segment are typically neighbours — which is why a PIN is a useful starting point for finding comparable properties.
Why it beats an address
Addresses are ambiguous and sometimes absent. Two towns share street names; new subdivisions get addresses from the village before the county splits the parcels, so a real, deliverable address can have no parcel of its own yet. The PIN is exact.
Where to find it
Your assessment notice, your tax bill, your deed, and your county's parcel search.
When it changes
Splits, combinations and new subdivisions create new PINs and retire old ones. If your PIN changed, comparisons to your own prior years need care — you may be looking at a different parcel. Ask the assessor for the history if the numbers do not line up.