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.

According to the U.S. Census Bureau, Loudoun County has a total area of 521 square miles (1,350 km2), of which 516 square miles (1,340 km2) is land and 6 square miles (16 km2) (1.1%) is water. 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 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

  • Fairfax County (east)
  • Prince William County (southeast)
  • Fauquier County (south)
  • Jefferson County, West Virginia (west)
  • Clarke County (west)
  • Washington County, Maryland (northwest)
  • Frederick County, Maryland (north)
  • Montgomery County, Maryland (east)

National protected area

  • Harpers Ferry National Historical Park

Traditionally a rural county, Loudoun’s population has grown dramatically since the 1980s. Having undergone heavy suburbanization since 1990, Loudoun has a full-fledged service economy. It is home to world headquarters for several Internet-related and high tech companies, including Verizon Business, Telos Corporation, Orbital Sciences Corporation, and Paxfire. Like Fairfax County’s Dulles Corridor, Loudoun County has economically benefited from the existence of Washington Dulles International Airport, the majority of which is in the county along its border with Fairfax.

Loudoun County retains a strong rural economy. The equine industry has an estimated revenue of $78 million. It is home to the Morven Park International Equestrian Center which hosts national horse trials. In addition, a growing wine industry has produced several internationally recognized wines. Loudoun County now has 40 wineries and over 25 active farms. Loudoun has rich soil and was in the mid-19th century a top wheat-producing county in the fourth largest wheat-producing state.

MCI, Inc. (formerly WorldCom), a subsidiary of Verizon Communications, is headquartered in Ashburn, Loudoun County. It announced it would move its headquarters to Ashburn in 2003. AOL had its headquarters at 22000 AOL Way in Dulles in unincorporated Loudoun County. In 2007 AOL announced it would move its headquarters from Loudoun County to New York City; it would continue to operate its Virginia offices. Orbital Sciences Corporation has its headquarters in Dulles.

Loudoun County houses over 60 massive data centers, many of which correspond to Amazon Web Services’s (AWS) us-east-1 region. These data centers are estimated to carry 70 percent of global web traffic.

Before its dissolution, Independence Air (originally Atlantic Coast Airlines) was headquartered in Dulles. At one time Atlantic Coast Airlines had its headquarters in Sterling. Before its dissolution, MAXjet Airways was headquartered on the grounds of Washington-Dulles International Airport.

The National Transportation Safety Board operates the Ashburn Aviation Field Office in Ashburn, an unincorporated area of Loudoun County. The Federal Aviation Administration’s Washington Air Route Traffic Control Center, the second-busiest facility of its kind in the nation, is located in Leesburg.

Emergency services are provided by the Loudoun County Fire and Rescue Department with the Office of Emergency Management. LCFR is a combination system that utilizes some 500 volunteers and over 600 career firefighters, EMT/paramedics, dispatchers, and support staff. LCFR is one of the largest fire and rescue systems in Virginia.

Law enforcement in Loudoun County is provided by the Loudoun County Sheriff’s Office, which is Virginia’s largest sheriff’s office, as well as three town police departments: Leesburg Police, Purcellville Police, and Middleburg Police. The county’s highways are also patrolled by Virginia State Police troopers. Dulles Airport and the Dulles Toll Road are patrolled by the Metropolitan Washington Airports Authority Police Department.

The Loudoun County Public Library System has eleven branches in the county. The library’s Outreach Department of the Loudoun County Public Library is a resource for those who cannot easily access branch services. The public library system has won several awards, including 10th place for libraries serving a comparably sized population in 2006

Loudon County is one of the counties in Virginia that elects to cover their employees in the Virginia Mortgage Assistance Program (VMAP). The program is designed to make housing more affordable for civil service workers in Virginia.

Loudoun County has two airports: Washington Dulles International and Leesburg Executive.

Loudoun County operates its own bus public transit system, known as Loudoun County Commuter Bus.

The Silver Line of the Washington Metro provides service at the Dulles Airport, Loudoun Gateway, and Ashburn stations.

Nearby Communities