No, it is explicitly not part of the official name.
The name of the city is "Washington." No more and no less.
The "District of Columbia" (or "DC") part is only generally added to disambiguate it (the city) from the state of Washington. It's is no more a part of the official name of the city than is "California" (or "CA") part of the official name of "Los Angeles."
The name of the city is "Washington." No more and no less.
The "District of Columbia" (or "DC") part is only generally added to disambiguate it (the city) from the state of Washington. It's is no more a part of the official name of the city than is "California" (or "CA") part of the official name of "Los Angeles."