---
title: "What Is an APN (Assessor’s Parcel Number)? APN Lookup by API | Realie"
description: "What an APN (assessor’s parcel number) is, how APN, AIN, PIN and SBL differ by county, why an APN needs a state and county, and how to look up a property by APN with Realie’s API, CLI or MCP."
canonical: https://www.realie.ai/info/what-is-an-apn
---

# What is an APN (assessor’s parcel number), and how do I look up a property by APN?

By Realie · Published 2026-11-12

## Quick Answer

An APN (assessor’s parcel number) is the number a county assessor assigns to each parcel of land for property tax records. Counties name and format it differently, and the same number can exist in two counties, so an APN identifies a parcel only together with its state and county. To look one up with Realie, send state, county and parcelId to the Parcel ID Lookup endpoint.

[Get a Realie API key](https://app.realie.ai/developer)

### Summary

Every county record about a property, from ownership and assessment to tax, sales and zoning, hangs off its parcel identifier. Each county assessor numbers its parcels in its own format and often under its own name: Los Angeles County uses a 10-digit AIN, Cook County, Illinois, a 14-digit PIN, and New York tax bills outside New York City a tax map number, also called the SBL. This page explains what the number encodes, why it needs a state and county, where the county FIPS code fits, and how to look up a property by APN with Realie’s REST API, CLI or MCP server.

## What an APN identifies

An APN points to one tax parcel: the unit of land the county assessor values and taxes. A parcel is not always a house. It can be vacant land, a multi-unit building or a commercial lot.

Most parcel numbers encode a location on the county’s tax maps. Los Angeles County’s 10-digit Assessor’s Identification Number (AIN) is a 4-digit map book number, a 3-digit page number and a 3-digit parcel number, written 1234-567-890. Cook County’s 14-digit Property Index Number (PIN) is area, subarea, block, parcel and a 4-digit unit, written AA-SS-BBB-PPP-UUUU, where a unit of 0000 means the parcel is not a condominium or leasehold unit.

Both counties print the number on the property tax bill, and Cook County says it is on the deed too.

## APN, AIN, PIN and SBL: local names for one idea

This page uses APN as the general term, but counties use their own names and layouts. Realie’s API calls the county’s number parcelId and returns it as the county assessor recorded it, for example "0314- -0009" for a parcel in the District of Columbia, so you can match it against records you already hold.

**Parcel number names and formats by county or state**

| Term | Used by | Format | What the parts mean |
| --- | --- | --- | --- |
| APN (assessor’s parcel number) | General term; Realie’s parcelId field | Varies by county | Whatever the county assessor assigns |
| AIN (Assessor’s Identification Number) | Los Angeles County, California | 10 digits, 1234-567-890 | Map book (4 digits), page (3), parcel (3) |
| PIN (Property Index Number) | Cook County, Illinois | 14 digits, AA-SS-BBB-PPP-UUUU | Area, subarea, block, parcel, unit; a unit of 0000 is not a condominium or leasehold unit |
| Tax map number (SBL) | New York State tax bills outside New York City | Section, block and lot | Also called the print key or tax map parcel; New York City bills use borough-block-lot (BBL) |

Names and formats are from each office’s own pages, linked under Sources and checked November 12, 2026. Other counties use other names and layouts; check with the county assessor.

## Why an APN needs a state and county, and where FIPS fits

An APN is unique only inside its county, and two counties can issue the same number. That is why Realie’s Parcel ID Lookup asks for state and county alongside a raw APN.

A county FIPS code identifies the county as a number. The U.S. Census Bureau gives each state a 2-digit code and each county a 3-digit code within its state; together they form the 5-digit county FIPS code, such as 11001 for the District of Columbia or 48453 for Travis County, Texas. Store FIPS codes and APNs as text, not numbers, because leading zeros matter.

Realie records carry the county FIPS code: countyFips ("11001") in the nested v3 response shape, and fipsState ("48") plus fipsCounty ("085") in the flat, v2-compatible shape.

Realie also combines the two into one string, realieParcelId: the 5-digit county FIPS code, a hyphen, then the APN with spaces written as ~. The District of Columbia parcel 0314- -0009 becomes 11001-0314-~-0009. Because the FIPS prefix names the county, a realieParcelId can be looked up on its own, without state or county.

## How to look up a property by APN with Realie

REST: call GET /api/public/property/parcelId with state, county and parcelId, and send your API key in the Authorization header. Pass the county by name, for example TRAVIS. The response is one property record that carries the parcel, assessor and recorder fields together.

```bash
curl -H "Authorization: YOUR_API_KEY" "https://app.realie.ai/api/public/property/parcelId/?state=TX&county=TRAVIS&parcelId=R12345"
```

If you stored a realieParcelId, pass it as parcelId with no state or county: parcelId=48453-R12345.

CLI: realie parcel takes the same state, county and parcel ID, or a realieParcelId on its own. Add --json for machine-readable output.

```bash
realie parcel --parcel-id "R12345" --state TX --county TRAVIS
realie parcel --parcel-id "48453-R12345"
```

MCP: the parcel_lookup tool calls the same endpoint, so an agent in Claude, Cursor or another MCP host looks up an APN the same way. REST, the CLI and MCP share one parameter catalog.

Only a successful 200 response counts as a call. A 400 means a required parameter is missing or the ID could not be parsed; 400, 401, 403 and 404 responses are not billed.

For lookups by address, owner name or location, see [How do I query county parcel data by API?](https://www.realie.ai/info/how-to-query-county-parcel-data-by-api).

## When the APN you hold does not match exactly

APNs get retyped, exported from spreadsheets and reformatted between systems, so dashes, spaces and leading zeros drift. Realie’s Parcel ID Lookup tries the exact value first. If that misses, it retries within the same county with punctuation removed, and an APN made only of digits is also tried with common zero-padding variants, so a number that lost a leading zero in a spreadsheet can still match.

If a variant matches more than one parcel, the API returns 409 Conflict instead of guessing. A 409 is not billed; retry with the APN exactly as printed on the tax bill, or look the property up by its address.

Parcels also split, merge and get renumbered over time. [Where can I search county parcel data?](https://www.realie.ai/info/county-parcel-data-search) covers why parcel IDs drift and how to reconcile older records.

## Sources

- [Realie Parcel ID Lookup (v3 API reference)](https://docs.realie.ai/api-reference/v3/property/parcel-id-lookup)
- [Realie v3 OpenAPI specification](https://docs.realie.ai/api-reference/v3/openapi.json)
- [Realie v3 property data schema (parcelId, realieParcelId, countyFips)](https://docs.realie.ai/api-reference/v3/property-data-schema)
- [Realie flat property data schema (fipsState, fipsCounty)](https://docs.realie.ai/api-reference/property-data-schema)
- [Realie CLI](https://docs.realie.ai/realie-cli)
- [Realie API response codes](https://docs.realie.ai/api-reference/response-codes)
- [Los Angeles County: the Assessor’s Identification Number (AIN) on the tax statement](https://www.propertytax.lacounty.gov/Home/AnnualSecuredPropertyTaxInformationStatement)
- [Cook County Clerk: about the Property Index Number (PIN)](https://www.cookcountyclerkil.gov/property-taxes/about-property-index-number-pin)
- [New York State Department of Taxation and Finance: property tax bill examples](https://www.tax.ny.gov/pit/property/star/sample-tax-bills.htm)
- [U.S. Census Bureau: ANSI and FIPS code lists](https://www.census.gov/library/reference/code-lists/ansi.html)

## Frequently asked questions

### What is a parcel ID number?

Another name for the APN: the number the county assessor uses to identify one tax parcel. Counties also call it an AIN, a PIN, a tax map number or an SBL. Realie returns it in the parcelId field, as the county assessor recorded it.

### APN vs PIN vs AIN: what is the difference?

They do the same job under local names. Los Angeles County calls its 10-digit number an AIN (map book, page, parcel). Cook County, Illinois, calls its 14-digit number a PIN (area, subarea, block, parcel, unit). APN is the general term. The format changes by county; the role does not.

### How do I search a property by parcel number?

Send state, county and the parcel number to Realie’s Parcel ID Lookup, GET /api/public/property/parcelId, or run realie parcel --parcel-id "R12345" --state TX --county TRAVIS in the CLI. A stored realieParcelId such as 48453-R12345 works on its own.

### Is an APN unique across the United States?

No. An APN is unique only within its county, and two counties can use the same number. Pair it with the state and county, or with the 5-digit county FIPS code, as Realie’s realieParcelId does.

### Where do I find a property’s APN?

On the county property tax bill, and often on the deed. If you only have the street address, look the property up with Realie’s address endpoint; the record it returns includes the parcelId and the county FIPS code.

## Related Questions

- [How do I query county parcel data by API?](https://www.realie.ai/info/how-to-query-county-parcel-data-by-api)
- [Where can I search county parcel data?](https://www.realie.ai/info/county-parcel-data-search)
- [What is parcel boundary data, and how is it different from assessor data?](https://www.realie.ai/info/parcel-boundary-data)
- [Where can I access county level property records?](https://www.realie.ai/info/county-level-property-records)
- [How do I choose a property data API, and what should I test before I sign?](https://www.realie.ai/info/how-to-choose-a-property-data-api)