| Zip codes are used by the US Postal Service to | | | | is as follows: |
| make mail delivery more efficient. The basic | | | | - 0 - Connecticut, Massachusetts, Maine, New |
| format of US zip codes consists of five numbers. | | | | Hampshire, New Jersey, Puerto Rico, Rhode |
| The first three numbers represent the sectional | | | | Island, Vermont, US Virgin Islands, Army Post |
| center facility and the other digits represent the | | | | Europe, Fleet Post Office Europe |
| older postal code for a specific state or city. The | | | | - 1 - Delaware, Pennsylvania and New York |
| process of using postal coded for US cities came | | | | - 2 - District of Columbia, Maryland, North Carolina, |
| into effect in 1943, but in 1963, zip codes came | | | | South Carolina, Virginia, and West Virginia |
| into use for the whole country. | | | | - 3 - Alabama, Florida, Georgia, Mississippi, |
| The sectional center facility part of the zip code is | | | | Tennessee, Army Post Office Americas, Fleet |
| the center for processing the mail. Here the mail | | | | Post Office Americas |
| is sorted according to the first three digits of the | | | | - 4 - Indiana, Kentucky, Michigan and Ohio |
| zip code and sent to the respective centers in | | | | - 5 - Iowa, Minnesota, Montana, Montana, North |
| each location. These digits identify the centers all | | | | Dakota, South Dakota and Wisconsin |
| over the country. In the individual centers, the | | | | - 6 - Illinois, Kansas, Missouri and Nebraska |
| mail is then sorted according to the last three | | | | - 7 - Arkansas, Oklahoma, Texas and Louisiana |
| digits and sent to the post offices where the | | | | - 8 - Arizona, Colorado, Idaho, New Mexico, |
| addressees pick up their mail. Sectional centers do | | | | Nevada, Utah and Wyoming |
| not deliver mail and are not open to the public. | | | | - 9 - Alaska, American Samoa, California, Guam, |
| Up until 1967, second and third class mail did not | | | | Hawaii, Marshall Islands, Federated States of |
| require a zip code. After that date however, it | | | | Micronesia, Northern Mariana Islands, Oregon, |
| became mandatory for all mail to have the proper | | | | Palau, Washington, Army Post Office Pacific, and |
| zip code in the address. In 1983, the US further | | | | the Fleet Post Office Pacific. |
| expanded the zip code feature making it the Zip | | | | The zip codes can also be divided and changed |
| Code + 4. These four digits were then used to | | | | when a rural area becomes a suburb of a larger |
| identify a specific geographical area. In the SCF, a | | | | city. The new codes become effective once they |
| machine identifies the zip code and sorts the mail | | | | are announced, but there is a grace period to |
| so that it goes to the correct post office. | | | | allow the residents to get used to their new zip |
| Today the first digits of the zip code identify the | | | | code. When a city expands so that the sectional |
| state or SCF. The second and third digits identify | | | | facility cannot handle all the mail coming through it, |
| a region of the state and the fourth and fifth | | | | it is sometimes necessary to open a new facility, |
| numbers identify a specific address in that region. | | | | which then receives its own number. This also |
| The main town gets the zip code and then the | | | | changes the zip code for the people living in that |
| surrounding towns follow in numerical order. | | | | area. |
| The allocation of the first number in the zip code | | | | |