How to Look Up a Zip Code

Zip code search
Search zip code databases.

This article explains how to do a zip code search. Before we describe the process and refer you to some online tools, let’s talk about zip codes. The word ZIP in Zip Code stands for “Zone Improvement Plan”. The United States Postal Service established the numerical codes to designate a local area or entity for the delivery of mail by a postal carrier.

ZIP Codes may consist of 5, 7, 9, or 11 digits and may refer to a street section, a collection of streets, an establishment, a structure, or a group of post office boxes.

While the numbers are rarely a key piece of information in an investigation, it is helpful for private investigators to have an understanding of the codes to help conduct more effective address searches. Private investigators who specialize in skip tracing and locating missing persons would benefit from having a good knowledge of the codes and of various zip code search tools and websites.

List of Zip Code Search Tools

Many websites allow you to conduct searches 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 lookup 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, includes other data and Mexico and Canada as well.
  • Melissa Data – Melissa is an excellent resource that has a number of helpful online search forms. For example, you can use their Personator search to enter an address and get the name, phone number, and email of the owner 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.

Also, the site has a handy tool that provides a list of 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 Code Directory

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

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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