Arlington County is an urban county located in the Commonwealth of Virginia, in the United States, separated from Washington DC by the Potomac River. Originally, part of the District of Columbia, the land now occupied by the county, was returned to Virginia on July 9,1846 through a congressional law that took effect in 1847. As of January 1,2006, it had an estimated population of 200,226 inhabitants. Strictly speaking, it is not appropriate to refer to the city of Arlington. All cities within the state are independent of the counties, although these could be incorporated into the counties.
However, Arlington has not been incorporated because the laws of Virginia prevent the creation of a new municipality within a county that has a population greater than 1,000 inhabitants per square mile.