You’ve got the history right. According to D.C. historian John Muller, the District of Columbia Organic Act of 1801 bit off chunks of Maryland and Virginia to create a “Ten Miles Square” District of Columbia; the Virginia portion was ceded back in the 1840s. Through much of the 19th century, the historic L’Enfant City was known widely as Washington City; Georgetown was Georgetown; and the sparsely populated suburbs of the remainder of the District were called Washington County. When Ulysses S. Grant was elected president and set about readmitting the Confederate states to the Union, there was an effort to form new state governments, and the District of Columbia Organic Act of 1871 repealed the individual charters of the District’s three component entities and created a unified city government.

Colloquially, people began referring to the new city as “New Washington.” But officially? Georgetown, says D.C. historian Don Hawkins, “became a convenient designation for the neighborhood, but its official use was limited to its designation as an official port of entry.” And Washington City and Washington County ceased to have any official use.

According to Cynthia Brock-Smith, secretary of the District of Columbia, the 1871 act referred only to the District of Columbia, and so that is the official name of the jurisdiction. (The District seal adopted in that year, bearing just the words “District of Columbia” and “Justitia Omnibus,” remains the city’s seal to this day.) “We refer to it as Washington, D.C., but the legal name is the District of Columbia,” Brock-Smith says. “We can’t find anything that officially says ‘Washington, D.C.’ in our records.” But she notes that there’s one written use of “Washington, D.C.” that remains widespread: as a postal address.