U.S. POSTAL CODE DIRECTORY

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Using ZIP Codes for Demographic Research

U.S. ZIP Codes Guide · Updated November 2026

ZIP Codes are often used as convenient geographic labels when organizing demographic or market research. They can help group records, compare broad areas, and create an initial view of regional patterns.

Postal areas are not always stable statistical units. Their boundaries and coverage may differ from census geographies, and some ZIP Codes do not represent residential populations. For formal analysis, consider Census ZIP Code Tabulation Areas (ZCTAs) and document how records were matched.

For address-specific mailing decisions, verify the complete delivery address with the United States Postal Service (USPS). This directory is provided as a general reference.

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ZIP codes are a system of postal codes used by the United States Postal Service (USPS) since 1963. The term ZIP, an acronym for Zone Improvement Plan, is properly written in capital letters and was chosen to suggest that the mail travels more efficiently, and therefore more quickly, when senders use the code in the postal address. The basic format consists of five decimal numerical digits. An extended ZIP+4 code, introduced in the 1980s, includes the five digits of the ZIP code, a hyphen, and four more digits that determine a more precise location than the ZIP code alone. The term ZIP code was originally registered as a servicemark (a type of trademark) by the U.S. Postal Service, but its registration has since expired.

ZIP codes designate only delivery points within the United States and its dependencies, as well as locations of its armed forces. There are no ZIP codes reserved for designating mail bound for foreign destinations (with the exception of U.S. military units stationed outside of the United States), and therefore, international outbound mail should not include a ZIP code in the delivery address. The last line of a foreign address must only show the name of the country of destination.

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