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Decoding ZIP Codes: The numbers have meaning

November 3, 2009
Provided by DEBRA MITCHELL, U.S. Postal Service

The U.S. Postal Service launched the Zoning Improvement Plan (ZIP) Code in 1963 to better handle increasing volumes of mail. Its numbers are easy to understand.

The first number in the code represents a general geographic area of the nation, "0" in the East, moving to "9" in the West. The next two numbers represent regional areas, and the final two identify specific Post Offices. The lowest number ZIP Code is 00501, a unique ZIP for the Internal Revenue Service in Holtsville, NY. The highest number ZIP Code (99950) is in Ketchikan, AK.

The ZIP+4 Code was introduced in 1983. The extra four numbers allow mail to be sorted to a specific group of streets or to a high-rise building. In 1991, two more numbers were added so that mail could be sorted directly to a residence or business.

Today, the use of ZIP Codes extends far beyond the mailing industry and they are a fundamental component in the nation's 911 emergency system.

The Postal Service maintains a data base for zip code information and it is the responsibility of any business who uses this data to update their records from postal sources frequently because zip codes can and do change to meet the needs of the Postal Service for sorting mail.

For more information about purchasing stamps, stamps by mail, postal regulations, a free subscription to USA Philatelic magazine, Post Office events, the location of the nearest postal store or contract unit, or for answers to your specific Postal Service questions, contact USPS at

1-800-275-8777, or visit To schedule a presentation for our community, club or group on how the Postal Service brings the Post Office to your home or office computer, call 239-573-9638.



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