Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area. Principal Cities: Washington, DC; Arlington, VA; Alexandria, VA; Reston, VA; Bethesda, MD; Frederick, MD; Gaithersburg, MD; Rockville, MD. Counties: Frederick County, Montgomery County, District of Columbia, DC; Calvert County, MD; Charles County, MD; Prince George's County, MD; Arlington County, VA; Clarke County, VA; Fairfax County, VA; Fauquier County, VA; Loudoun County, VA; Prince William County, VA; Spotsylvania County, VA; Staffor