It's barely a thought anymore, unless you're sending something through the US Postal System, about your zip code.  The five-digit sequence, which can be expanded to nine with a hyphen, is the last part of your address to make sure your mail gets to you.  Have you wondered why the system was created and how the individual codes came to be?

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When Were Zip Codes Created

The system that would eventually result in the zip code system we use today was created over 80 years ago.  In 1943 the Department of the Post Office created the Postal Zone system.  It was necessitated by the loss of thousands of postal workers to service in World War II and the hiring of inexperienced clerks.

Photo Smithsonian National Postal Museum
Photo Smithsonian National Postal Museum

It was decided that a system needed to be created due to the increase in mail being handled and to make it easier on the large number of replacement clerks.

Postal Zones

The Postal Zone system came into being to address those issues.  It began as a one or two digit code, depending on the area, intending to improve accuracy and efficiency of sorting mail.  the zones were created to service the largest cities in the country, so it was not a "universal" system.  It did achieve it's purpose and was met with little resistance in those cities.  The Postal Zone system lasted for 20 years until need, again, became the agent of change.

Photo Smithsonian National Postal Museum
Photo Smithsonian National Postal Museum

The Zip Code System

In 1962, then US Postmaster General James Edward Day, declared the Postal Zone system was outdated and a new system needed to be created.  By 1960 the Postal services was handling around 66 billion pieces of mail per year.  The growth of suburban communities created the need for change so the Zone Improvement Plan was created and has been used ever since.

So What Do Tri-Cities Zip Codes Represent?

This is what the numbers in the five-digit code represent:

  1. The first number determines the 9 is the far west region of the US
  2. The next two numbers define the central post office facility in the far west region.  So all mail for the Tri-Cities comes from the central post office facility identified as 93.
  3. The final two numbers identify small post offices and also can be identifiers for postal zones.  So Kennewick has three different identifiers 36, 37, and 38 for central post office facility 93; Richland has two 52 and 54; Pasco has two as well 01 and 02.
Photo by Justin Sullivan/Getty Images
Photo by Justin Sullivan/Getty Images

What's Up With Those Other Four Numbers?

The last four numbers you see after a hyphen were created in 1983 with the idea of speeding up mail sorting by machines.  The first two numbers after the hyphen stand for the delivery sector and the last two are for delivery segment.  The idea was to get as specific as the floor in an office building.  The last four numbers never really caught on and are only really used by companies that do mass mailing.

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