William County is located in the Commonwealth of Virginia and is part of the Washington metropolitan area. Its county seat is the independent city of Manassas.

The county government is headed by a Board of County Supervisors, which is composed of seven members elected from single-member districts. The county is also served by a number of constitutional officers, including a sheriff, a commonwealth's attorney, a treasurer, and a commissioner of the revenue.

William County is included in the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area. It is bounded on the north by Loudoun and Fairfax Counties, on the west by Fauquier County, on the south by Stafford County, and on the east by Prince George's County, Maryland.

The county is home to several important military installations, including Marine Corps Base Quantico, the FBI Academy, and the National Geospatial-Intelligence Agency. It is also home to several large employers, including the government contractor BAE Systems, the defense contractor General Dynamics, and the health care provider Inova Health System.

For the most up-to-date and in-depth information, please check the public records links below.