Manassas's an independent city within the confines of Prince William County in the Commonwealth of Virginia. The population was 35,135 at the 2000 census. The Bureau of Economic Analysis combines the city of Manassas (along with Manassas Park) with Prince William County for statistical purposes. The City of Manassas's part of the Washington Metropolitan Area and's situated in the Northern Virginia region. History In 1861, the First Battle of Manassas – also known as the First Battle of Bu… (More on Manassas)