An APN, or Assessor's Parcel Number, is the unique identifier a county assessor assigns to every parcel of land it taxes. It is the county's primary key for real property: the tax bill, the ownership record, the permit history, and the recorded deeds all hang off it. Every parcel has exactly one, and it is public information you can look up for free in about a minute.
Addresses are for mail. Parcel numbers are for records. That distinction is the whole reason the APN exists, and once you have worked with county data for a while it stops being a formality and starts being the only field you trust. Addresses get renumbered, misspelled, abbreviated four different ways, and assigned to buildings that do not exist yet. The parcel number just sits there.
This is a glossary entry inside the public records guide for real estate. If you want the map tool that displays parcel numbers geographically, that is county GIS parcel maps.
What the digits mean
There is no national format. Each county invented its own, and most encode geography in the digits.
The common pattern is a hierarchy that narrows from big to small: a map book or township, then a page or section, then a block, then the individual parcel. The Los Angeles County Assessor uses a 1234-567-890 format, where the first four digits are the map book, the next three the page, and the last three the parcel on that page. That structure is why neighboring parcels usually have near-identical parcel numbers, and why a sorted list of APNs is roughly a geographic tour.
Washington does it more plainly. King County's identifier is a PIN: a ten-character string built from a six-character MAJOR plus a four-character MINOR, per the county's own parcel extract documentation. The major is the plat or subdivision, the minor is the lot within it. Snohomish County uses a 14-digit PARCEL_ID. Pierce County calls the field TaxParcelNumber and runs ten characters.
The practical consequence: never assume a parcel number format, and never strip the leading zeros. A parcel number is a string, not an integer. Excel converting 0123456789 to 123456789 has broken more county data joins than any other single cause I know of, mine included.
What your county calls it instead
"APN" is the dominant term in the West, and roughly half the country calls it something else. All of these mean the same thing.
| Term | Where you will see it |
|---|---|
| APN (Assessor's Parcel Number) | California and much of the West; the default term nationally |
| PIN (Parcel Identification Number) | Washington, Illinois, North Carolina, and others |
| Parcel Number / Tax Parcel Number | The generic form, used almost everywhere |
| Folio Number | Florida, notably Miami-Dade |
| Property ID / Account Number | Texas appraisal districts and parts of the Southeast |
| Property Index Number | Cook County, Illinois |
| Strap Number | Parts of Florida |
| Sidwell Number | Parts of the Midwest, from the mapping company that drew them |
If a form asks for one term and your county publishes another, they are the same number. Paste it in.
Four free ways to find a parcel number
Ranked by how fast they actually work.
1. The county assessor's parcel search. Search "[county name] assessor parcel search," open the county-domain result, and search by street address. The parcel number is on the record it returns, usually at the top. This takes under two minutes in most counties and is the route I use by default. The county-by-county portal directory is in property owner search by county.
2. The county GIS parcel viewer. Zoom to the property, click the parcel, and read the number off the popup. Slower than the assessor's search for a single lookup, and much better when you do not have a clean address, when the property is a vacant lot with no address at all, or when you want the neighboring parcels too.
3. Your own paperwork, if you own it. The parcel number is printed on the property tax bill, on the deed, on the title report, and on the closing statement. The tax bill is the easiest place to find it.
4. The recorded deed. Washington requires the parcel number, or an abbreviated legal description, on the first page of a recorded document under RCW 65.04.045. Most states have a comparable cover-page rule, so pulling the deed from the recorder gets you the number even when the assessor's site is down.
Skip the sites that charge for an "APN lookup." Every county in the country publishes this for free, and the paid tools are reselling the county's own record.
Where you actually need it
For a single house, you often do not. For anything at volume, it is the field that makes the work possible.
- Permit and code enforcement systems. Some municipal systems index cases by parcel, not by address. This is not a footnote. Three of the municipal code enforcement sources I ingest publish their cases with a parcel number and no street address field at all, which means the parcel number is the only way to learn where the case is. Resolve the parcel against the county layer or you have a list of case numbers pointing at nothing.
- Joining datasets. Assessor, sales, permits, and violations only line up cleanly on the parcel number. Joining on address means normalizing "123 NORTH 45TH STREET APT 2" against "123 N 45th St #2" and accepting the errors that survive.
- Recorded documents. Deed and lien searches take the parcel number directly, and it beats a name search when the owner is an entity.
- Ordering title. Title companies want the parcel number, and giving them one avoids the round trip.
- Buying vacant land. Raw land often has no address. The parcel number is the only identifier it has.
Parcel numbers are not permanent
This one surprises people, and it is the most useful thing on this page.
When a parcel is split, merged, short-platted, or subdivided, the county retires the old parcel number and issues new ones. The old number does not get reassigned to something else; it goes dead. Any list keyed to it silently stops matching, and nothing errors out.
The counties are open about this in their data. Pierce County's tax parcel layer carries a RetiredDate field on every record. Snohomish County's parcel layer carries STATUS, where anything other than active means the parcel no longer exists as mapped, plus its own RETIREDATE. If you are pulling parcel data on a schedule, filter on those fields or you will carry ghosts for years.
Practical rule: a parcel number is stable for as long as the parcel is. Treat it as a strong identifier, not an eternal one, and re-resolve any list older than a year or two.
Why we match on address anyway
Worth being straight about, since it cuts against everything above.
Our database keys properties on a normalized address, not a parcel number. That is a deliberate trade. We ingest code violation data from ten municipal systems across three counties, and those systems do not agree on whether to publish a parcel number, which county's format it is in, or whether to zero-pad it. Address is the one field nearly all of them do publish, so address normalization is where the matching effort goes. It is documented, it is tested, and it is the reason address normalization matters so much to the accuracy of the lists we produce.
The cost of that choice is real. Address matching loses records that a parcel join would have caught, particularly on multi-unit buildings and on properties whose city address differs from the county situs address. Where a source publishes a parcel number and no address, we resolve it through the county parcel layer first and then match on the address that comes back.
I am not telling you address matching is better. I am telling you which one your data actually supports, and for a lot of municipal sources the answer is address, whether you like it or not.
Frequently asked questions
What does APN stand for?
Assessor's Parcel Number. Some counties write it as Assessor Parcel Number or Assessor's Parcel Identification Number. Same thing.
Is an APN the same as a parcel number?
Yes. "APN," "parcel number," "tax parcel number," "PIN," and "folio number" are regional names for the same county-assigned identifier. Which term you see depends on the county, not on the type of record.
How do I find the APN for an address for free?
Search the county assessor's parcel database by address. It is free in essentially every county and returns the parcel number along with owner, assessed value, and property characteristics. If the address search fails, use the county GIS parcel viewer and click the property on the map.
Can two properties have the same APN?
No. Within a county, a parcel number identifies exactly one parcel. Across counties, numbers repeat constantly, which is why any multi-county dataset has to key on county plus parcel number rather than parcel number alone. A single parcel can hold several buildings and several units, and they all share the one number, which is exactly why unit-level records are hard to key this way.
Does the APN change when a property is sold?
No. A sale changes the owner, not the parcel. The parcel number changes only when the parcel itself changes: a split, a merge, a subdivision, or a boundary line adjustment. A house that sells five times keeps the same number through all five.
Where is the parcel number on my property tax bill?
Near the top of the first page, usually in the same block as the property address and the account information. It may be labeled parcel number, PIN, account number, or APN depending on the county.