One Loudoun is a census-designated place in Loudoun County, Virginia, United States. It is a mixed-use development just south of Virginia State Route 7, 29 miles northwest of Washington, D.C., and 7 miles southeast of Leesburg. One Loudoun was developed since the 2010 census, so it was not recognized as a census-designated place until the 2020 census. The community has an Ashburn mailing address. As of the 2020 census, the population was 2,285.