What is an APN (Assessor's Parcel Number)?

By Leo Yong · Last updated April 26, 2026 · 11 min read

An APN (Assessor's Parcel Number) is a unique identifier assigned to every parcel of real property by the county tax assessor's office. Think of it as a Social Security number for land: every lot, tract, or unit gets its own number so the county can track ownership, assess taxes, and maintain property records.

Why APNs Matter

APNs are the primary key across property systems:

• Tax assessment: The assessor uses APNs to link each parcel to its tax bill
• GIS mapping: Parcel polygon layers are keyed by APN for spatial queries
• Title records: Deeds and ownership transfers reference APNs
• Public notice mailings: Radius searches return parcels by APN, which you match to owner and mailing data
• Permit tracking: Building permits and planning cases link to the affected parcel's APN

APN Formats Vary by County

There is no national standard for APN format. Each county designs its own numbering system. Real-world examples:

How APNs Are Constructed

Most APN formats encode a hierarchy that mirrors how the county's parcel maps are organized. Knowing the structure helps when you have a partial APN or need to find neighboring parcels.

Map-book / Book-page formats (most California counties)

An APN like 5043-018-025 decodes as:

• 5043: Map book number. The assessor maintains physical (or digital) books of plat maps; this number identifies which book.
• 018: Page within the book. Each page covers a section of the county.
• 025: The 25th parcel on that page.

Parcels with the same first two segments are geographic neighbors. 5043-018-024 and 5043-018-026 are next-door neighbors of 5043-018-025.

PLSS-based formats (most Midwest / public-land-survey counties)

States surveyed under the Public Land Survey System encode the township-section grid into the APN. Cook County, IL's 17-03-123-045-0000 decodes as:

• 17: Township (T17N or similar)
• 03: Section number within the township
• 123: Block within the section
• 045: Lot within the block
• 0000: Sub-parcel suffix (often condos or units)

Sequential / serial formats

Counties like Harris (TX) and King (WA) skip geographic encoding and assign sequential integers. These don't reveal anything about location; you need the GIS layer to map APN to coordinates.

Folio / BBL formats (FL, NYC)

Florida's Folio Number and NYC's Borough-Block-Lot (BBL) embed the municipality or borough as the leading segment. Two parcels with the same leading number are in the same political subdivision.

Common APN Problems & How to Handle Them

1. Leading zeros get stripped

If you paste 0420590010014 into Excel or a script that auto-types it as a number, it becomes 420590010014: twelve digits instead of thirteen. Lookups fail. Store APNs as strings, not numbers. In Excel, format the column as Text before pasting.

2. Dashes don't match between sources

The tax bill shows 5043-018-025. The GIS layer stores 5043018025. The county website search tolerates both, but a programmatic API may not. When a query fails, try the alternate format. UrbanKit Studio's Parcel Lookup Tool normalizes both sides automatically.

3. APNs change when parcels are split or merged

If a developer splits one parcel into three, the original APN is retired and three new APNs are issued. If two parcels are merged, both originals are retired and a new combined APN is issued. Old deeds and title reports may reference retired APNs. Verify against current county records before using an APN for a public notice mailing.

4. Sub-parcels for condos and PUDs

A condo building has one "site APN" but each unit has its own APN with a sub-parcel suffix. A radius search might return only the site APN, missing the individual unit owners that need notification. Check the county's documentation for how condos are represented.

5. Mineral rights, easements, and air rights

In some Western states (TX, OK, NM) mineral rights are tracked as separate parcels with their own APNs, even though they overlap surface parcels. For public notice, you typically need only surface parcels; verify with the county.

6. ROW (right-of-way) parcels are often unowned

Streets, alleys, and railroad rights-of-way may have APNs assigned to a public agency or "ROW" placeholder owner. They show up in radius searches but don't need notification mail. Filter out parcels owned by the county, the state, or labeled "ROW."

APN vs. Other Property Identifiers

You may encounter several related terms that aren't identical:

• APN (Assessor's Parcel Number): Assigned by the county assessor for tax purposes. The most common identifier used in GIS and planning.
• PIN (Parcel Identification Number): Often used interchangeably with APN, but in some states (like Illinois) it's a distinct numbering system.
• Tax ID / Tax Account Number: The number on your tax bill. Usually the same as the APN, but some counties use a separate billing number.
• Legal description: A text description from a deed (e.g., "Lot 5, Block 3, Sunny Acres Subdivision"). Not the same as an APN but recorded alongside it.
• FIPS code: A federal code for the county itself, not for individual parcels.

How to Find Your APN

Several ways to look up a property's APN:

1. Property Tax Bill

Your annual property tax statement includes the APN, usually near the top. Look for labels like "Parcel Number," "APN," or "Tax ID."

2. County Assessor Website

Most county assessors have an online property search by address. The APN appears in the results. Search: [Your County] assessor property search

3. County GIS Map Viewer

Interactive GIS maps let you click on a parcel to see its APN and other attributes. Search: [Your County] GIS map

4. Title Documents

Your deed, title report, or title insurance policy includes the APN for the property.

Using APNs with Parcel Lookup Tools

When you use a parcel lookup tool, the APN is how you match query results to specific properties. County GIS layers include the APN as an attribute field, often named APN, PARCEL_ID, PIN, PARCELNO, TAXID, FOLIO, or PROPERTY_ID. The Parcel Lookup Tool auto-detects which field is the APN by reading the layer's metadata, so you can paste any county's ArcGIS REST URL and start querying.

International Equivalents to the U.S. APN

Most countries have an analogous parcel identifier. If you're working across borders or with international planning data, the concept translates as follows:

APN FAQ

Are APN and PIN the same thing?

In casual use, yes; both refer to the unique number identifying a parcel. APN (Assessor's Parcel Number) is the term used by tax assessors, while PIN (Parcel Identification Number) is the term used in some states (notably Illinois, Indiana, and parts of the Midwest). The same parcel will have one APN/PIN issued by the county that uses both terms interchangeably.

How long is an APN?

It varies. The shortest are 8-9 digits (some Midwest counties). The longest are 13-15 digits (Texas counties using full account numbers). Most California counties use 10-12 digits formatted as three groups separated by dashes.

Can two parcels have the same APN?

Within a single county, no. Across counties, yes; there's no national uniqueness guarantee. When you reference an APN, pair it with the county or state.

What's the difference between APN and street address?

APNs are stable identifiers tied to the legal parcel. They don't change with ownership transfers, but they DO change when parcels are split, merged, or remapped by the assessor (see "Common APN Problems" above). Addresses, by contrast, are assigned by the postal service or local government and can change with renumbering, road realignments, or annexations. A vacant lot has an APN but no address. A high-rise has many addresses (one per unit) but one APN for the building site.

Can I look up an APN by address?

Yes; most county assessor websites support address-to-APN lookup. The Parcel Lookup Tool also supports searching ArcGIS layers by any field, including address fields like SITUS_ADDR.

Why does my APN have leading zeros that disappear in spreadsheets?

Spreadsheets default to treating numeric-looking strings as numbers, which strips leading zeros. To preserve them, format the APN column as Text before pasting, or prepend a single quote ('0420590010014) to force text storage.

What field name does the APN use in a GIS layer?

Common field names: APN, PARCEL_ID, PARCELNO, PIN, FOLIO, TAXID, PROPERTY_ID, BBL (NYC), ASSESS_ID. The Understanding Parcel Data Fields article has a full glossary.

Related Resources

• Understanding Parcel Data Fields: Owner, Situs, APN & More
• How to Find Your County's ArcGIS Parcel Layer URL
• How to Query County Parcel Data by Owner Name via ArcGIS REST API: after you have the APN format down, this guide shows how to construct WHERE clauses that search by owner name across FeatureServer and MapServer endpoints
• How to Get Parcel GeoJSON Data from Your County GIS
• Public Notice Radius Requirements: What Varies by Jurisdiction