How to Look Up a Zip Code


This article explains how to do a zipcode search. Before we describe the process and refer you to some online tools, let’s talk about zip codes. ZIP codes, or Zone Improvement Plan codes, are postal codes used by the United States Postal Service (USPS) to deliver mail efficiently. They were introduced in 1963 to improve mail sorting and delivery. ZIP codes are five-digit numbers that help identify specific geographic areas, such as neighborhoods, cities, or towns. The first digit generally represents a group of U.S. states, the next two digits represent a region within that group, and the final two digits represent a more specific location, like a post office or a rural area. ZIP+4 codes add four additional digits to pinpoint delivery locations further. These codes are essential for accurate and efficient mail delivery across the United States.

While the codes are rarely a key piece of information in an investigation, understanding the codes can help private investigators conduct more effective address searches. For example, private investigators specializing in skip tracing and locating missing persons would benefit from a good knowledge of the codes, search tools, and websites.

List of Zip Code Search Tools

Many websites allow you to conduct and reverse zip code searches and lookups for free. Following is a list of recommended zip code search tools and websites:

  • United States Postal Service City State / ZIP Code Associations – Use the USPS website to look up zip codes by street address, city, and state or even find all codes within a particular state. You can also enter a company name to find its associated code.
  • – Includes people search tools such as white pages, yellow pages, public records searches, reverse search directories, area code searches, and more.
  • Intelius People Search – Public records and much more.
  • National Address Server – Enter an address and get the address with the Zip Code+4.
  • Zip Code Download – Accurate United States Postal Service databases, distance calculation tools, Mexico and Canada, and other data.
  • Melissa Data – Melissa is an excellent resource with many helpful online search forms. For example, you can use their Personator search to enter an address and get the owner’s name, phone number, and email in return. Melissa also has a nationwide people finder search that allows you to search by name, address, phone, or email and get the other information back in return. The site also has a handy tool that lists all the street names or house numbers within a particular mail code. This can be a handy tool for specialized research. They also have searches related to city information, maps, schools, and much more.

United States Post Office ZipCode Directory

The United States Post Office publishes the National 5-Digit Zip Code and Post Office Directory, which contains helpful information on how to find mailing codes and addresses. This volume, published in 2016, is the most recent by the USPS and comes as a two-volume set.

Dome Zip Code Directory

The Dome Zip Code Directory is an alphabetical list of cities and towns in the U.S. with detailed zip code maps of principal cities. The book features an updated area code directory with cross-references by city and state, the latest postal rates for domestic and foreign mail, and UPS information.

Questions and Comments

Please post any questions about the zip code search techniques below. See our other private investigator search tools.

Michael Kissiah is the owner of Brandy Lane Publishing, LLC, which owns and operates a small portfolio of websites, including Michael created more than 20 years ago after working as a private investigator in the state of Florida. Since that time, he has become an expert at how to find information online and has written over 1000 articles on topics related to the investigation industry. In addition, he is the author of the "Private Investigator Licensing Handbook", available at


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