Arlington County, Virginia area. The county is situated in Northern Virginia on the southwestern bank of the Potomac River directly across from Washington, D.C., of which it was once a part. With a land area of , Arlington is the geographically smallest self-governing county in the U.S., and by reason of state law regarding population density, has no incorporated towns within its borders. Due to the county's proximity to downtown Washington, D.C., Arlington is home to many important installations for the capital region and U.S. government, including the Pentagon, Reagan National Airport, and Arlington National Cemetery. Many schools and universities have campuses in
Arlington County, Virginia in the county, while 86% commute in, with 27% commuting from Fairfax County. An additional 92,784 people commute out for work, with 42% commuting to DC, and 29% commuting to Fairfax County. A number of federal agencies are headquartered in Arlington, including the Air Force Office of Scientific Research, American Battle Monuments Commission, DARPA, Diplomatic Security Service, Drug Enforcement Administration, Foreign Service Institute, the DHS National Protection and Programs Directorate, Office of Naval Research, Transportation Security Administration, United States Department of Defense, United States Marshals Service, and the United States Trade and Development Agency. Companies headquartered in Arlington include AES,