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USPS Zip Code – USPS Look Up a ZIP Code

USPS ZIP Code: The United States Postal Service (USPS) uses a type of postal code called a US ZIP code to better route mail within the country. The map above shows ZIP codes near me. ZIP codes are still referred to as US postal codes by some. Zone Improvement Plan is the acronym for the term ZIP. The basic format of five digits was first used in 1963. Later, it was expanded to include an additional four digits after a dash to create a ZIP+4 code. The USPS can more precisely group mail for delivery with the additional four digits. Even though the United States Postal Service (USPS) was the first company to use ZIP codes, many other shipping companies, including United Parcel Service (UPS), Federal Express (FedEx), and DHL, also use ZIP codes to sort packages and figure out how long it will take to ship a package (the shipping rate).

Types of USPS Zip Code:

  • Unique/single high volume address (ex. 20505 for the CIA in Washington, DC).
  • PO Box only (ex. 22313 for the PO Boxes of Alexandria, VA).
  • Military.
  • Standard (all other ZIP codes).

Assignment of ZIP codes and Mail Sorting

The first digit of a USA ZIP code typically represents a group of U.S. states. The map depicting the first digit of the above zip codes demonstrates that they are distributed from the north east to the west coast. The central mail processing facility, also known as a sectional center facility or a “sec center,” that is utilized to process and sort mail is identified by the first three digits of a ZIP code. All mail with the same first three digits is sent to the same security center first, where it is sorted by the last two digits and sent to local post offices. The sec centers typically complete the majority of sorting overnight and are closed to the public. The map of the first three digits of a zip code shows that the digits after the first are typically assigned from east to west as well. 0 is closer to white on the map, whereas 9 is much more vivid. Even though there are a few exceptions, such as the southwest tip of Georgia, which uses 39XXX like central Mississippi, it is simple to follow the gradient across each zone.

Although the ZIP+4 code is not required, it assists the post office in further mail sorting. A city block, a group of apartments, or an individual high-volume receiver might all be represented by a ZIP+4 code. Additionally, it is common for each PO Box number to be associated with a distinct ZIP+4 code. The last few digits of a PO Box number can sometimes be used to combine multiple PO Box numbers into a single ZIP+4 code. However, because this method is not universal, the ZIP+4 must still be looked up for each PO Box.

The map shows that not every place in the United States has a ZIP code. This is because some areas of the country are so remote that they do not have one. There are not enough addressable addresses in rural and remote areas of the country to establish a mail route. A ZIP is not required if mail delivery is not used. These areas are some of the most out of the way places in the country if you want to get away from it all.

ZIP Code Tabulation Areas (ZCTAs)

The Census Bureau of the United States developed tabulation areas for USPS ZIP codes. Statistics about places that most people are familiar with are conveyed by them. However, ZCTAs and ZIP codes are not identical. A ZIP code’s coverage area is difficult to precisely define, as previously mentioned. ZCTAs were created to precisely define a geographical area and account for some of the difficulties associated with assigning an area to a ZIP code. Additionally, ZCTAs are updated less frequently than ZIP codes. For the Census, they are typically updated once every ten years.

A ZCTA is given an area by the Census based on census blocks, which are the smallest geographic units used by the Census. As shown on the right, a typical census block is modeled after a city block. It is surrounded on all four sides by segments of city streets, each of which has its own name and address. The problem lies in the fact that census blocks almost always split in the middle of a street. Because it would require two postal workers, one for each side of the street, to deliver mail to that street, ZIP codes rarely exist. In the example, one mail carrier might deliver mail to all three sides of the block using a particular ZIP code, while another mail carrier might deliver mail to the opposite street using a different ZIP code. Because the census block is the area that is precisely measured, the Census Bureau will assign the entire block to a single ZCTA (in this case, 21044) when this occurs. Census block boundaries close to the edge of a ZIP code almost always divide ZIP codes if you get very precise (usually in meters, not miles).

Matching ZIP Codes with States, Counties, and Cities

Keep in mind that ZIP codes were created to facilitate faster mail delivery. They were not designed to match existing boundaries like states, cities, or even counties. The “boundary” of a ZIP code will cross state lines if it is more efficient for a mail carrier to drive across a state line to deliver mail. Some ZIP codes do cross state lines, though not all do (for example, 65733, 71749, and 73949). As part of our US ZIP code list, you can find the complete list of ZIP codes that cross state lines.

When attempting to assign a USPS ZIP code to a particular county (up to 25% cross county lines), congressional district, metro area, time zone, area code, etc., things get even more complicated. Most of the time, the boundaries’ edges meet. We typically list either the most common region for the ZIP code or multiple regions if there are more than one in the ZIP code for the purposes of our free zip code database by county downloads.

The assignment is slightly more difficult for cities. The city where the ZIP code is located is not always used by the US Postal Service. It is more general to assign cities to ZIP codes. The primary post office is typically referred to as the city. For instance, nearly every ZIP code in Missouri’s St. Louis County includes the city of Saint Louis, despite the fact that the name of the smaller city in which they are located is more appropriate.

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