Loudoun County 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. The county seat is Leesburg. Loudoun County is part of the Washington–Arlington–Alexandria, DC–VA–MD–WV Metropolitan Statistical Area.

Leesburg is a town in and the county seat of Loudoun County, Virginia, United States. Its is part of both the Northern Virginia region of the state and the Washington metropolitan area, including Washington, D.C., the nation's capital.Settlement in the area began around 1740, which is named for the Lee family, early leaders of the town. Located in the far northeast of the state, in the War of 1812 it was a refuge for important federal documents evacuated from Washington, DC, and in the Civil War, it changed hands several times.