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

Published: March 2026 • 6 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 used 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 then match to owner/mailing data
  • Permit tracking — Building permits and planning cases are linked 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. Here are some real-world examples:

County Example APN Format
Los Angeles, CA 5043-018-025 Map Book–Page–Parcel
Maricopa, AZ 123-45-678 Book–Map–Parcel
King County, WA 1234567890 10-digit sequential
Cook County, IL 17-03-123-045-0000 Township–Section–Block–Lot–Suffix
Harris County, TX 0420590010014 13-digit sequential
Dashes, spaces, or no separators? Some counties include dashes in the "official" APN while their GIS system stores it without separators. When querying a parcel database, try both formats if your first attempt returns no results.

APN vs. Other Property Identifiers

You may encounter several terms that are related but not identical:

  • APN (Assessor's Parcel Number) — Assigned by the county assessor for tax purposes. This is 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

There are several ways to look up a property's APN:

1. Property Tax Bill

Your annual property tax statement always 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 where you can look up parcels by address. The APN will be shown 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 will include the APN for the property.

APNs can change: When parcels are subdivided, merged, or adjusted, the county assigns new APNs. Always verify you're using the current APN, especially for older properties or recent developments.

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 typically include the APN as an attribute field—often named APN, PARCEL_ID, PIN, PARCELNO, or TAXID. Our Parcel Lookup Tool lets you search by APN to retrieve parcel geometry and owner information directly from your county's data.

Ready to look up parcels by APN?

Try the Parcel Lookup Tool →

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