Unique ZIP Code
A ZIP code assigned exclusively to a single organization or entity that receives a high volume of mail, such as a government agency or large corporation.
The USPS assigns unique ZIP codes to organizations that receive enough daily mail volume to warrant their own dedicated code. Examples include the IRS processing center in Ogden, Utah (84201), the Empire State Building in New York (10118), and many federal agencies in Washington, D.C.
Unique ZIP codes simplify internal mail sorting for the recipient and allow the USPS to route large volumes directly without intermediate sorting steps. They are not associated with a geographic delivery area in the traditional sense.
Because unique ZIP codes do not represent residential populations, the Census Bureau excludes them when building ZIP Code Tabulation Areas (ZCTAs). Databases that map ZIP codes to demographic data typically show zero population for unique ZIPs.