Abbreviations
Q. In running text, what is the preferred way to write “Washington, D.C.”?
A. When using the traditional form of abbreviation—that is, with periods, D.C.—use commas:
Washington, D.C., was built on what was essentially swampland.
When using the abbreviations recommended by the US Postal Service, commas may be omitted:
To me, Washington DC is first and foremost the home of the Smithsonian.
