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. 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 mail delivery 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 specializing in skip tracing and locating missing persons would benefit from a good knowledge of the codes and various zip code 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.

Also, the site 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 Code Directory

The United States Post Office publishes the National 5-Digit Zip Code and Post Office Directory. 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 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.


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