Arlington County is a county in the Commonwealth of Virginia coterminous with the U.S. Census Bureau's census-designated place of Arlington, which is the second-largest principal city of the Washington metropolitan area in the United States. As a result, the county is often referred to in the region simply as "Arlington" or "Arlington, Virginia". In 2016, the county's population was estimated at 230,050, making it the sixth-largest county in Virginia, or the fourth-largest city if it were incorporated as such. It is the highest-income county in the U.S. by median family income, and has the highest concentration of singles in the region.
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 26 square miles (67 km2), 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, most prominently the Antonin Scalia Law School of George Mason University.
When Congress arrived in the new capital, they passed the Organic Act of 1801 to officially organize the District of Columbia and placed the entire federal territory, including the cities of Washington, Georgetown, and Alexandria, under the exclusive control of Congress. Further, the unincorporated territory within the District was organized into two counties: the County of Washington to the east of the Potomac and the County of Alexandria to the west. It included all of the present Arlington County, plus part of what is now the independent city of Alexandria. This Act formally established the borders of the area that would eventually become Arlington but the citizens located in the District were no longer considered residents of Maryland or Virginia, thus ending their representation in Congress
In 1920, the Virginia legislature renamed the area Arlington County to avoid confusion with the City of Alexandria which had become an independent city in 1870 under the new Virginia Constitution adopted after the Civil War.
In the 1930s, Hoover Field was established on the present site of the Pentagon; in that decade, Buckingham, Colonial Village, and other apartment communities also opened. World War II brought a boom to the county, but one that could not be met by new construction due to rationing imposed by the war effort.
In October 1942, not a single rental unit was available in the county. On October 1, 1949 the University of Virginia in Charlottesville created an extension center in the county named Northern Virginia University Center of the University of Virginia, then University College, next Northern Virginia Branch of the University of Virginia, then George Mason College of the University of Virginia, and today George Mason University. The Henry G. Shirley Highway (now Interstate 395) was constructed during World War II, along with adjacent developments such as Shirlington, Fairlington, and Parkfairfax.
CNN Money ranked Arlington as the most educated city in 2006 with 35.7% of residents having held graduate degrees. Along with five other counties in Northern Virginia, Arlington ranked among the twenty American counties with the highest median household income in 2006. In 2009, the county was second in the nation (after nearby Loudoun County) for the percentage of people ages 25–34 earning over $100,000 annually (8.82% of the population). In August 2011, CNN Money ranked Arlington seventh in the country in its listing of "Best Places for the Rich and Single."
In 2008, 20.3% of the population did not have medical health insurance. In 2010, AIDS prevalence was 341.5 per 100,000 population. This was eight times the rate of nearby Loudoun County and one-quarter the rate of the District of Columbia.
Arlington National Cemetery is an American military cemetery established during the American Civil War on the grounds of Confederate General Robert E. Lee's home, Arlington House (also known as the Custis-Lee Mansion). It is directly across the Potomac River from Washington, D.C., north of the Pentagon. With nearly 300,000 graves, Arlington National Cemetery is the second-largest national cemetery in the United States.
Arlington House was named after the Custis family's homestead on Virginia's Eastern Shore. It is associated with the families of Washington, Custis, and Lee. Begun in 1802 and completed in 1817, it was built by George Washington Parke Custis. After his father died, young Custis was raised by his grandmother and her second husband, the first US President George Washington, at Mount Vernon. Custis, a far-sighted agricultural pioneer, painter, playwright, and orator, was interested in perpetuating the memory and principles of George Washington. His house became a "treasury" of Washington heirlooms.