Loudoun County (/ˈlaʊdən/) is in the northern part of the Commonwealth of Virginia in the United States. In 2020, the census returned a population of 420,959, making it Virginia’s third-most populous county. Loudoun County’s seat is Leesburg. Loudoun County is part of the Washington–Arlington–Alexandria, DC–VA–MD–WV Metropolitan Statistical Area. As of 2020, Loudoun County had a median household income of $147,111. Since 2008, the county has been ranked first in the U.S. in median household income among jurisdictions with a population of 65,000 or more.