Arlington County is a county in the Commonwealth of Virginia. It is coterminous with the U.S. Census Bureau-census-designated place of Arlington, which is the second-largest principal city of the Washington metropolitan area. As a result, the county is often referred to in the region simply as "Arlington" or "Arlington, Virginia".
It is the highest-income county in the United States by median family income, though it has the highest concentration of singles in the region. According to a 2016 study by Bankrate.com, Arlington is the best place to retire, with nearby Alexandria coming in at second place. Criteria of the study included cost of living, rates of violent and property crimes, walkability, health care quality, state and local tax rates, weather, local culture and well-being for senior citizens. In 2002, Arlington received the EPA's National Award for Smart Growth Achievement for "Overall Excellence in Smart Growth." In 2005, the County implemented an affordable housing ordinance that requires most developers to contribute significant affordable housing resources, either in units or through a cash contribution, in order to obtain the highest allowable amounts of increased building density in new development projects, most of which are planned near Metrorail station areas.