Arlington County is a county in the Commonwealth of Virginia, and 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 2016, the county's population was estimated at 230,050, making it the sixth-largest county in Virginia, or the fourth-largest city if it were incorporated as such. It is the highest-income county in the United States by median family income, and has the highest concentration of singles in the region. The county is situated in Northern Virginia on the southwestern bank of the Potomac River directly across from Washington, D.C., of which it was briefly a part. With a land area of , Arlington is the geographically smallest self-governing county in the United States, and by reason of state law regarding population density, has no incorporated towns within its borders. Due to the county's proximity to downtown Washington, D.C., Arlington is home to many important installations for the capital region and US government, including the Pentagon, Reagan National Airport, and Arlington National Cemetery. Many schools and universities have campuses in Arlington, most prominently the Antonin Scalia Law School of George Mason University.
Does it have highest numbers of married couples?
and has the highest concentration of singles in the region.