What Is an APN?
By AcreBound Editorial Team Updated:
Quick Answer
An APN, or Assessor’s Parcel Number, is the number a county assessor assigns to a parcel of land so it can be found in tax and property records. It identifies the land, not the building or the owner, and an ordinary sale doesn’t normally change it.
Each county sets its own format, and the number can change if the parcel is split or merged.
An APN, short for Assessor's Parcel Number, is the number a county assessor gives to a parcel of land so it can be found in tax and property records. It identifies the land itself, not the building on it and not the person who owns it.
Street addresses make poor identifiers. They change, one address can cover several parcels, and vacant land often has none. A parcel number sidesteps all of that, which is why tax bills, deeds, title reports and county maps lean on it.
What an APN Looks Like
There is no national format. Each county, and in some states each taxing office, builds its own numbers and picks its own name for them. These three offices publish how theirs work:
| Place | What it's called | How it's built |
|---|---|---|
| Maricopa County, AZ | Parcel number (APN) | Book, map and item, plus a letter if the parcel was split. Example from the assessor: 111-11-111-A |
| Los Angeles County, CA | Assessor's Identification Number (AIN) | Ten digits: map book, page and parcel. Example from the treasurer: 1234-567-890 |
| New York State | Tax map number, also called SBL (section-block-lot) or print key | The state tells taxpayers to enter it exactly as printed on the bill, including periods and hyphens |
Those examples are formats, not real parcels. Don't try to guess a number for a property. Look it up.
Reading one: a Maricopa County example
Maricopa County's assessor explains its numbers piece by piece. In a number like 111-11-111-A, the first three digits are the assessor's book, which covers a large part of the county. The next two are the map within that book. The last three are the item, meaning the specific property. A letter after them shows which piece of a split parcel you're looking at.
That book-page-parcel logic is common. A University of California extension program notes that parcel maps used to be printed in map books, which is why many California APNs read like a location in those books. Other places may use plain sequential numbers, so don't assume every APN can be decoded.
What an APN Is Not
- It isn't an address. Several addresses can sit on one parcel, and a parcel can have no address at all.
- It isn't tied to an owner. The number stays with the parcel, and an ordinary sale doesn't normally change it.
- It isn't the legal description. The deed's legal description is what defines the land. Many deeds carry the APN too. San Diego County's recorder, for one, lists the APN among its requirements for deeds under a local ordinance. See Legal Description vs Street Address vs APN.
- It isn't always the only number on the bill. On a Los Angeles County tax bill, for example, the PIN is a code for online transactions, not a parcel number.
Who Uses APNs
- County assessors and tax collectors to value property and send tax bills.
- Title and escrow companies to make sure they are working on the right parcel.
- Agents and land buyers to look up a property when there is no reliable address.
- Surveyors, utilities and planners to point at one parcel in documents and maps.
Does Every Property Have One?
Nearly every taxable parcel has some kind of parcel number. Government-owned and other exempt land may be tracked differently. A new parcel gets its number after it's created, so a lot that was just split or approved may not exist in every system yet.
Los Angeles County's assessor is open about this lag on its mapping help page. Its parcel layer is refreshed once a year, after the annual roll release in July, so parcels created by deeds, new subdivisions or condominiums don't appear on that map until the next release.
Can an APN Change?
Yes, when the land changes. Splitting a parcel, merging parcels or a county renumbering its maps can all produce new numbers. Maricopa's split letter is one visible trace of this.
Picture a 1998 deed that lists an APN for a 20-acre parcel. The land was later divided in two. Search the old number today and you may get nothing, or only one half. Search the address or the owner's name instead, or ask the assessor's office whether the number was retired and what replaced it. A street address can change while the APN stays put, and the reverse can happen too.
Can You Search a Property by APN?
Often, but it depends on the office. Maricopa's assessor says its search accepts a parcel number in any format, with or without separators. Other systems are pickier, so enter it as printed and then try again without hyphens. Include the county, because two counties can use the same number for different parcels.
Even inside one county, different offices can work differently. San Diego County's recorder removed APN search from its online record search on December 9, 2024, citing a California state law (AB 1785). APN searches there are now only available at in-person kiosks. If one site refuses your number, the assessor's site or a parcel map may still take it.
To get the number in the first place, see How to Find the APN for a Property. For land with no address, see How to Find a Property That Has No Street Address.
Common Mistakes
- Copying an account number, PIN or other code from the bill instead of the parcel number.
- Leaving out the county.
- Dropping leading zeros or the split letter at the end.
- Trusting an old APN after a split or merge.
Frequently Asked Questions
Is an APN the same as a parcel ID?
Usually, yes. Counties use different labels for the same kind of number. The exceptions and look-alikes are covered in APN vs Parcel ID.
Does the APN change when a property is sold?
An ordinary sale doesn't normally change it. It changes when the parcel itself changes, for example through a split or merger.
How many digits does an APN have?
It depends on the county. Los Angeles County uses ten digits for its AIN, while Maricopa County builds its number from book, map and item parts with an optional letter.
Where is the APN on a tax bill?
Usually near the top, labeled Parcel No., APN, parcel ID or something close. Maricopa's assessor also prints it on the Notice of Value.
Can I find the owner from an APN?
Often, through the county assessor's record or a parcel map. What's shown differs by county. See How to Find Out Who Owns a Property.
AcreBound can also search by APN. Here's more on APN search, and on what a parcel map shows.
Sources
- Maricopa County Assessor: Frequently Asked Questions How a parcel number is built; search formats.
- Los Angeles County Treasurer and Tax Collector: General Request for Information Definition of the AIN and of the bill PIN.
- Los Angeles County Assessor: Mapping help Map update schedule; PINs.
- New York State Tax Department: Property tax bill examples Tax map number, SBL and print key.
- San Diego County Assessor/Recorder/County Clerk: Recording APN on deeds; APN search change.
- UC ANR Informatics and GIS Program: Finding and Using Parcel Data in California APN structure and map books.