Arlington County is located across the Potomac River from Washington, D.C. The County was at one point part of the District of Colombia, but for various reasons it was returned to Virghinia in 1847.
Arlington has been ranked both the most walkable city(2005) as well as the most educated in the country(2006.) Other honors include safest city in which to weather a recession(2008), second best place for the rich and single(2009) and best city for families in the country (2010.) Wikipedia entry for Arlington.