Parcel Return Service, DC

ZIP code 56999 is located in Washington, DC, housing the iconic headquarters of the United States Postal Service. Situated at 475 L'Enfant Plaza SW, this ZIP code serves as the central hub for mail processing and distribution services in the nation's capital. The area is also home to the National Mall, a historic park dotted with monuments and museums, making it a significant cultural and administrative center in the city.