Prince William County is located in Northern Virginia approximately 35 miles southwest of Washington, DC. It is bounded on the north by Fairfax and Loudoun Counties, on the east by the Potomac River (Maryland), on the south by Stafford County and on the west by Fauquier County.

     Prince William County encompasses a total area of 348 square miles (222,684 acres) and a total land area of 338 square miles (216,269 acres).  Prince William County includes within its boundaries the independent cities of Manassas and Manassas Park. The combined area of Prince William County and the independent cities is 360 square miles (230,626 acres). Federal land accounts for 41,671 acres (18.8% of the total area) and includes Quantico Marine Corps Base, Manassas National Battlefield Park and Prince William Forest Park. Prince William County includes four incorporated towns and fourteen census designated places, that is, unincorporated population centers that are designated by the U.S. Census Bureau for data collection purposes.

     Prince William County's highest elevation is 1,280 feet above sea level on Bull Run Mountain along its western boundary with Fauquier County; its lowest natural elevation is at sea level along the Potomac River, and its lowest man-made elevation is 15 feet below sea level at a quarry site near Manassas. The geographic center of the County is located near Brentsville at 38.55 degrees N. Latitude and 77.40 degrees W. Longitude.

     Prince William County is located in Northern Virginia approximately 35 miles southwest of Washington, DC. It is bounded on the north by Fairfax and Loudoun Counties, on the east by the Potomac River (Maryland), on the south by Stafford County and on the west by Fauquier County.

     Prince William County's highest elevation is 1,280 feet above sea level on Bull Run Mountain along its western boundary with Fauquier County; its lowest natural elevation is at sea level along the Potomac River, and its lowest man-made elevation is 15 feet below sea level at a quarry site near Manassas. The geographic center of the County is located near Brentsville at 38.55 degrees N. Latitude and 77.40 degrees W. Longitude.