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.
As of 2023, Loudoun County had a median household income of $156,821, the highest of any county or county equivalent in the nation.
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History
18th century
thumb|William and Sarah Nettle House in [[Waterford, Virginia|Waterford]]
Loudoun County was established in 1757 from Fairfax County. The county is named for John Campbell, Fourth Earl of Loudoun and governor general of Virginia from 1756 to 1759.
At the time of the American Revolution, Loudoun County was Virginia's most populous county. It was also rich in agriculture, and the county's contributions of grain to George Washington's Continental Army earned it the nickname "Breadbasket of the Revolution."
19th century
War of 1812
During the War of 1812, important federal documents and government archives were evacuated from Washington and stored at Leesburg. Local tradition holds that these documents were stored at Rokeby House.
U.S. president James Monroe treated Oak Hill Plantation as a primary residence from 1823 until his death on July 4, 1831. The Loudoun County coat of arms and flag, granted by the English College of Arms, memorialize the special relationship between Britain and the United States that developed through his Monroe Doctrine.
American Civil War
The American Civil War divided the county, which saw fighting because of its strategic location. In April 1861, both of Loudoun County's representatives to the Virginia Secession Convention of 1861 favored the Union. Delegates elected John Janney, a former Quaker and slave owner, presided over that assembly, which ultimately voted to secede. Loudoun voters also voted to secede. In addition to Confederate cavalry and infantry units formed within the county, other Loudoun residents traveled to Maryland to join Union army cavalry and border guard units. On October 21, 1861, in the Battle of Ball's Bluff along the Potomac River near Leesburg, future jurist Oliver Wendell Holmes Jr. was critically wounded.
In the spring of 1862, Leesburg was occupied by Union troops and later recaptured by the Confederate Army after Union troops withdrew. Confederate partisan John S. Mosby based his operations in Loudoun and adjoining Fauquier County.
In June 1863, during the Gettysburg campaign, Confederate major general J.E.B. Stuart and Union cavalry clashed in the battles of Aldie, Middleburg, and Upperville. By December 1863, Loudoun was held by Union forces, and was among the nine counties which elected delegates to the Virginia General Assembly at Alexandria.
Loudoun voters elected and reelected John J. Henshaw and J. Madison Downey as their representatives to that body, and fellow delegates elected Downey as their Speaker. Loudoun voters elected and reelected William F. Mercer to the upper body of that version of the Virginia General Assembly, and elected him to the Virginia Senate in the 1865–1867 session. They elected former delegates R.M. Bentley and William Hill Gray as their part-time delegates in the lower house in that session.
20th century
During World War I, Loudoun County was a major breadbasket for supplying provisions to soldiers in Europe. Loudoun farmers implemented new agricultural innovations such as vaccination of livestock, seed inoculations and ensilage. The county experienced a boom in agricultural output, outputting an annual wheat output of 1.04 million bushels in 1917, the largest of any county in Virginia that year. 1.2 million units of home produce were produced at home, much of which went to training sites across the state such as Camp Lee. The Smith–Lever Act of 1914 established increased agricultural education in Virginia counties, increasing agricultural yields. After the war, a plaque was dedicated to the "30 glorious dead" from the county who died in the Great War. Five of the thirty died on the front, while the other twenty five died while in training or in other locations inside the United States.
In 1962, Dulles International Airport was built in southeastern Loudoun County in Sterling. Since then, Loudoun County has experienced a high-tech boom and rapid growth. Accordingly, many have moved to eastern Loudoun and become residents of planned communities such as Sterling Park, Sugarland Run, Cascades, Ashburn Village, and Ashburn Farm, making that section a veritable part of the Washington suburbs. Others have moved to the county seat or to the small towns and rural communities of the Loudoun Valley, which makes up the majority of the county's area. It is bounded on the north by the Potomac River; across the river are Frederick, Washington and Montgomery counties in Maryland; it is bounded on the south by Prince William and Fauquier counties, on the west by the watershed of the Blue Ridge Mountain across which are Jefferson County, West Virginia and Clarke County, and on the east by Fairfax County. The Bull Run Mountains and Catoctin Mountain bisect the county. To the west of the range is the Loudoun Valley. Bisecting the Loudoun Valley from Hillsboro to the Potomac River is Short Hill Mountain.
Adjacent counties
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- Fairfax County (east)
- Prince William County (southeast)
- Fauquier County (south)
- Jefferson County, West Virginia (west)
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- Clarke County (west)
- Washington County, Maryland (northwest)
- Frederick County, Maryland (north)
- Montgomery County, Maryland (east)
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National protected area
- Harpers Ferry National Historical Park