When you need to send a letter, you might not think about it, but you must include a zip code with the address before you can mail the document successfully. 

This hasn’t always been the case, but now it seems like something that we couldn’t do without. 

They help your mail and packages get exactly where they need to get, so you don’t have to worry about it arriving at the proper place. 

There isn’t an elaborate story on how they came to be, but it is something that is essential to know, so you can understand why you must use them. 

Have you ever taken the time to wonder where zip codes come from? 

Keep reading for more information on the topic.

Here's a quick rundown of our list:

Adoption of Zip Codes

Must Read: San Diego County CA Zip Codes

They have not been around forever, but they have been used for a number of years. 

In the mid-20th century, as the mail service became more popular, it became clear that there had to be a way to organize everything, in order to make it easier to sort mail and make sure it was delivered to the right place.

At first, special codes were just being used in the most populated areas of America.

However, codes for the whole country became very necessary when many mail carriers had to go overseas to fight in World War II. 

The postal system, as well as many other industries, was understaffed, so there needed to be a better way to streamline the entire process.

There simply wasn’t a lot of time to go through the mail and sort it. 

Thus, ZIP codes were born, although they were not the modern type we still use today. 

Our modern zip codes were adopted starting in 1963. 

This is around the same time that the shortened state codes started to be used as well.

ZIP, or Zone Improvement Plan, codes are not just for cities and states though. 

If any place is large enough, it may have its own zip code. 

This includes places like airports or college campuses, as well as large corporations. 

Zip codes have been used in the past to help determine property values, and figure out whether or not a neighborhood is a desirable place to live. 

You can probably think of a few zip codes that you know of that prove this point. 

Of course, this isn’t the only thing you need to know about zip codes though.

You may also be wondering why they are 5 digits long.

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What the 5 Numbers Mean

Each digit has its own special meaning, and is a code to pinpoint the location.

The first number indicates the major region of the country, essentially the state that an address is in.

The second and third numbers are specialized according to your smaller region, like a central mail-processing center in your area.

Finally, the last 2 numbers are codes that signify the post office that is closest to you. 

Sometimes there are 4 additional digits that are added to the end of your zip code. 

These numbers narrow down your location even further. 

They don’t have to be used each time someone sends you a letter or bill, but it helps when it comes to keeping everything in order. 

You should know the extra 4 digits for your zip code, as you might need them for a number of reasons.

Depending on how large the area you live in is, there can be many zip codes in a location. 

You can look at a map of how these zip code zones are determined here

This is the reason that there are many zip codes in San Diego County, since it is a rather large area.

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Here’s a look at all of them. 

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They can help you determine what properties are available in certain neighborhoods or part of the county you want to live in. 

What do you think?

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Quite a big list - have I missed any in San Diego. 

Leave a comment below - or, call/text me at (760) 297-4539

Your Zip Insider, 

Scott

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