Post Office & Address Search
The United States Postal Service (USPS) delivers to more than 167 million addresses across all 50 states, D.C., Puerto Rico, and U.S. territories. The USPS maintains the official database of valid U.S. addresses and ZIP codes. ZIP code accuracy is critical for public-records research — many county, state, and federal databases use ZIP codes as a primary geographic identifier. This page provides direct links to official USPS tools for address verification, ZIP code lookup, post office locator, and mail tracking. Updated March 2026.
ZIP Code Lookup Tools
- USPS ZIP Code™ Lookup — The official USPS tool for finding ZIP codes. Search by address, city/state, or company name. Returns ZIP+4 (nine-digit) codes for precise mail routing and records searching.
- USPS PostalPro – ZIP Code Lookup — Business-focused version of the ZIP Code lookup tool.
- Census Bureau Geocoder — Converts addresses to coordinates and FIPS geographic codes (including county and census tract) — useful when ZIP codes span multiple counties.
Find Post Office Locations
- USPS Post Office Locator — Find the nearest post office, contract postal unit, or self-service kiosk by address or ZIP code. View hours, services, and parking information.
- USPS PO Box Finder — Find available PO Boxes by ZIP code, view sizes and current rental rates.
Address Validation & CASS Certification
Address validation ensures that a mailing address is deliverable by USPS standards. CASS (Coding Accuracy Support System) is the USPS certification for address-matching software. Validated addresses include the ZIP+4 code and delivery point barcode — critical for bulk mail automation rates.
- USPS Business Mail 101 – Address Validation — Official guide to validating address lists for business mailings.
- Smarty.com – USPS Address Verification Guide — How to use USPS tools for free address validation.
- Firstlogic Address Verification Tool — Free web-based single-address CASS verification tool.
USPS Mail Tracking & Delivery Services
- USPS Package Tracking — Track any USPS package with a tracking number. Supports Priority Mail, First-Class Package, Parcel Select, Media Mail, and Certified Mail.
- USPS Informed Delivery — Free daily email preview of incoming mail and packages. Also alerts for packages scheduled for delivery that day.
- USPS Priority Mail — 1–3 business day delivery with free tracking and insurance up to $50.
- USPS Postage Price Calculator — Calculate exact postage for any mail class, weight, size, and destination.
Address Change & Mail Forwarding
- USPS Change of Address (Mover's Guide) — Official USPS online change-of-address form. Costs $1.10 for identity verification. Set up mail forwarding from your old address for up to 12 months.
- USPS National Change of Address (NCOA) — Business service for updating mailing lists against USPS's database of 160+ million address changes over the past 48 months.
Frequently Asked Questions
What is a ZIP+4 code and why does it matter?
A ZIP+4 code is the standard five-digit ZIP code plus a four-digit extension that identifies a specific block, building, or P.O. Box. ZIP+4 codes enable automated sorting and precise delivery — and are required for presorted First-Class and bulk-rate discounts. For public-records research, ZIP+4 can narrow a search to a specific city block.
Can I look up who lives at a specific address?
Not through USPS (they do not publish resident information). However, property records at the county assessor's office show the registered owner of record for any property. Voter registration records (public in most states) may include residents. People-search services like Whitepages aggregate opt-in public data.
How do I find out if an address is a real, deliverable address?
Use the USPS ZIP Code Lookup tool and enter the full address. If USPS returns a standardized address with a ZIP+4 code, the address is deliverable. If no result is returned, the address may not exist or may be improperly formatted.
What is USPS Informed Delivery and is it free?
Yes, Informed Delivery is a free USPS service that sends a daily email with scanned images of incoming letter-sized mail and alerts for expected packages. Sign up at informeddelivery.usps.com. Available to verified residential address holders.
Page updated: March 2026