ZIP Code
Zone Improvement Plan code — a 5-digit postal code used by the United States Postal Service (USPS) to identify delivery areas.
ZIP codes were introduced on July 1, 1963, to improve mail sorting and delivery efficiency across the United States. The acronym stands for Zone Improvement Plan, a name chosen to suggest that mail travels more efficiently when senders include the code. The first digit designates a broad geographic region (0 for the Northeast, 9 for the West Coast), the second and third digits identify a sectional center facility (SCF), and the final two digits pinpoint a specific post office or delivery zone.
ZIP codes do not always correspond to contiguous geographic boundaries. Some are assigned to single high-volume addresses (such as large office buildings), PO Box ranges, or military installations overseas. The USPS periodically adds, retires, and reassigns ZIP codes as population patterns shift.
As of 2024, there are roughly 41,700 active ZIP codes in the United States, covering the 50 states, the District of Columbia, Puerto Rico, the U.S. Virgin Islands, Guam, American Samoa, and other territories.