In the District of Columbia you may vote early at your local election office by casting an "absentee" ballot in person. 

You may do this beginning 14 days before Election Day and continuing up through the day before Election Day.

In the District of Columbia you must have an excuse, such as age, disability, or absence from the area on Election Day, to vote absentee early in person.  

For more information, contact your local election office - link at right sidebar.