Find who owns any property — or every property a person or LLC owns — across major US counties, sourced directly from county assessor open data.
The National Property Owner Lookup API resolves property ownership from official county assessor records. Run a forward lookup (which owner is on a given street address) or a reverse lookup (every parcel a person or LLC owns within a county) — ideal for skip-tracing, real estate due diligence, lead generation, and CRM data enrichment. Each result is a normalized record with the owner name, situs address, parcel identifier, property type, assessed value, year built, and — where the county publishes it — the owner's mailing address and owner-occupancy flag. Coverage currently spans New York City, Philadelphia, Washington DC, and Boston, with more counties added over time; call the /counties endpoint for the live list. Every county returns the identical response shape, so you integrate once and get new markets for free.
/owner/countiesReturn the counties currently supported. Use the returned slug values for the county parameter on /lookup and /portfolio.
{
"count": 4,
"counties": [
{ "slug": "nyc", "name": "New York City, NY", "state": "NY" },
{ "slug": "philadelphia", "name": "Philadelphia, PA", "state": "PA" },
{ "slug": "washington-dc", "name": "Washington, DC", "state": "DC" },
{ "slug": "boston", "name": "Boston, MA", "state": "MA" }
]
}/owner/lookupForward lookup — find the owner(s) of a property by street address. The address is matched as a case-insensitive substring against the county assessor roll, so a partial address may return several parcels.
| Name | Type | Required | Description |
|---|---|---|---|
address | string | Required | Street address to look up (e.g. "350 Fifth Ave") |
county | string | Required | County slug from /owner/counties (e.g. "nyc", "philadelphia", "washington-dc", "boston") |
limit | number | Optional | Max matching records to return (1-100, default 25) |
{
"county": "nyc",
"address": "350 5 Avenue",
"count": 1,
"results": [
{
"county": "nyc",
"state": "NY",
"owner_name": "EMPIRE STATE REALTY OP LP",
"address": "350 5 AVENUE",
"city": "MANHATTAN",
"zip_code": "10118",
"parcel_id": "1000477501",
"property_type": "O4",
"assessed_value": 286000000,
"year_built": 1931,
"owner_mailing_address": null,
"owner_occupied": null
}
]
}/owner/portfolioReverse lookup — find every property owned by a person or LLC within a county. Powers skip-tracing and portfolio analysis. Owner name is matched as a partial, case-insensitive substring.
| Name | Type | Required | Description |
|---|---|---|---|
name | string | Required | Owner name or LLC to search (partial match, e.g. "CENTRAL CAPITAL GROUP") |
county | string | Required | County slug from /owner/counties |
limit | number | Optional | Max properties to return (1-200, default 50) |
{
"county": "philadelphia",
"owner_query": "CENTRAL CAPITAL GROUP",
"count": 1,
"results": [
{
"county": "philadelphia",
"state": "PA",
"owner_name": "CENTRAL CAPITAL GROUP LLC",
"address": "2124 E LEHIGH AVE",
"city": "PHILADELPHIA",
"zip_code": "19125",
"parcel_id": "314249400",
"property_type": "COMMERCIAL",
"assessed_value": 295000,
"year_built": 1925,
"owner_mailing_address": "1500 MARKET ST PHILADELPHIA PA 19102",
"owner_occupied": null
}
]
}