Middleburg is a town in Loudoun County, Virginia, United States, with a population of 673 as of the 2010 census. It is the southernmost town along Loudoun County's shared border with Fauquier County. Middleburg is known as the "Nation's Horse and Hunt Capital" for its foxhunting, steeplechases, and large estates. The Middleburg Historic District, comprising the 19th-century center of town, is listed on the National Register of Historic Places.