Arlington County is a county containing 207,627 residents, as of 2010, in the Commonwealth of Virginia. It is located directly across the Potomac River from Washington, D.C., and the two of them are linked by several highway and railroad bridges. A major airport of Washington, D.C., Ronald Reagan Washington National Airport, many Federal Government offices, including those of the Department of Defense, the Department of the Navy, the Drug Enforcement Agency, Arlington National Cemetery, and DARPA are located in Arlington County.The county was originally founded as Alexandria County on February 27, 1801 by passage of the District of Columbia Organic Act of 1801. Alexandria County along with the now-defunct Washington County were the two counties formed on that date within the District of Columbia. Due to issues involving congressional representation, abolition and economic decline, the county along with the then-Town of Alexandria were returned to the Commonwealth of Virginia in an act of the U.S. Congress which took effect in 1847. In 1920 the General Assembly of Virginia changed the name of the county to "Arlington County" in order to avoid confusion with Alexandria, which had become an independent city in 1870.

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