Loudoun County is located in the Commonwealth of Virginia. As of 1 July 2013, the population was estimated to be 347,969, making the county the third-most populous in Virginia. Loudoun County's county seat is Leesburg. As of 2007, the town had been county seat for 249 of the last 250 years.
As of 2011, Loudoun County had a median household income of $119,134. The county has been ranked number one in median household income since 2007 for jurisdictions in the United States with a population of 65,000 or more.