Alexandria County was created in 1800 when the District of Columbia was formed, retroceded to Virginia in 1846, and renamed Arlington County in 1920
Source: US Geological Survey (USGS), Mount Vernon 30x30 topographic quadrangle (1897)
Virginia's counties were created to meet the needs of the English settlers, based on English laws and customs. The Native Americans had their own way of organizing their territories, but after 1607 the English "tassantassas" (strangers/aliens) imposed their own sense of order upon the political landscape.
Counties come, counties go. The General Assembly has created at least 167 counties since 1634. The last one was "Virginia's Baby," created in 1880 and named Dickenson County.
There are only 95 counties remaining in Virginia now. Yohogania County was ceded to Pennsylvania. Illinois County was ceded to the new United States under the Articles of Confederation, when Virginia was willing to trade its land claims to the Northwest Territory beyond the Ohio River in order to increase support for the new national government.
Ten counties were "lost" when Kentucky became an independent state in 1790. Another 50 counties were incorporated in the new state of West Virginia in 1863. Ten counties have been abolished, with their land incorporated within the boundaries of other counties with other names or into independent cities.
In addition to elimination of some counties, four counties have changed their names since original creation by the General Assembly. One name, Rappahannock, was applied to a county which was abolished, then reused later and applied to a different county.
five counties in Hampton Roads that existed in 1848 have now "disappeared"
Source: Library of Congress, A map of the internal improvements of Virginia (by Claudius Crozet, 1848)
Virginia Counties That Changed Their Name
Alexandria (renamed Arlington County in 1920, to reduce confusion with City of Alexandria)
Charles River (renamed York County in 1643, to honor the King Charles I's son, the Duke of York)
Dunmore (renamed Shenandoah County in 1788, to avoid honoring the last English governor of the colony)
Warrosquyoake (renamed Isle of Wight County in 1637, to replace a Native American name)
Virginia-Created Counties That Are Now Extinct
Elizabeth City County
Virginia-Created Counties That Are Now in Kentucky
Virginia-Created Counties That Are Now in Pennsylvania
Virginia-Created Counties That Are Now in Ohio, Indiana, Illinois, Michigan, Minnesota, and Wisconsin
Illinois County was ceded to the new United States and became the Northwest Territory
Map Source: ESRI, ArcGIS Online
Virginia-Created Counties That Are Now in West Virginia
Wyoming Yohogania (part)
Ohio and Monongalia counties are now part of West Virginia, while Yohogania County is extinct
Source: Wikipedia, Yohogania County, Virginia