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". In 2014, the county's population was estimated to be 229,302, which would make it the fourth-largest city in the Commonwealth if it were incorporated as such.