Prince William County, Virginia in the context of "Virginia State Route 28"

Fairfax County, officially the County of Fairfax, is a county in the Commonwealth of Virginia. With a population of 1,150,309 as of the 2020 census, it is the most populous county in Virginia, the most populous jurisdiction in the Washington metropolitan area, and the most populous location in the Washington–Baltimore combined statistical area. The county seat is Fairfax; however, because it is an independent city under Virginia law, the city of Fairfax is not part of the county.

The county is part of the Northern Virginia region and forms part of the suburban ring of Washington, D.C., the nation's capital. The county is predominantly suburban with some urban and rural pockets. It borders Montgomery County, Maryland to its north, Falls Church, Alexandria, Arlington County, and Prince George's County, Maryland to its east, Charles County, Maryland to its southeast, Prince William County to its southwest, and Loudoun County to its northwest.

Colonel Thomas Lee (c. 1690 – November 14, 1750) was a planter and politician in colonial Virginia, and a member of the Lee family, a political dynasty. Lee became involved in politics in 1710, serving in both houses of the Virginia General Assembly, and also held important positions as Naval Officer for the Northern Potomac Region and agent for the Northern Neck Proprietary. After his father died, Lee inherited thousands of acres of land as well as enslaved people in then-vast Northumberland and Stafford Counties in Virginia as well as across the Potomac River in Charles County, Maryland. These properties were developed as tobacco plantations. Northumberland County was later subdivided, so some of Lee's properties were in present-day Fairfax, Fauquier, Prince William, and Loudoun counties and counties in the present-day Northern Neck of Virginia.

When Lee married Hannah Harrison Ludwell in 1722, he benefited from the connections of the already established Harrison family of Virginia. A year later, he would become a member of the House of Burgesses. Arson destroyed Lee's home, he used money from Caroline of Ansbach and Britain to build Stratford Hall overlooking the Potomac River. Four years later, in 1733, he was appointed to the Governor's Council, the upper house of the General Assembly. In 1747, he founded the Ohio Company of Virginia with fellow Virginian colonists who wished to expand Virginia's territory into the Ohio River Valley. For less than a year, in 1749 until his death in 1750, Lee served as the de facto royal governor of Virginia in place of the absent William Gooch.

The First Battle of Bull Run, called the Battle of First Manassas by Confederate forces, was the first major battle of the American Civil War. The battle was fought on July 21, 1861, in Prince William County, Virginia, just north of what is now the city of Manassas and about thirty miles west-southwest of Washington, D.C. The Union army was slow in positioning themselves, allowing Confederate reinforcements time to arrive by rail. Each side had about 18,000 poorly trained and poorly led troops. The battle was a Confederate victory and was followed by a disorganized post-battle retreat of the Union forces.

Just months after the start of the war at Fort Sumter, the northern public clamored for a march against the Confederate capital of Richmond, Virginia, which was expected to bring an early end to the Confederacy. Yielding to political pressure, Brigadier General Irvin McDowell led his unseasoned Union army across Bull Run against the equally inexperienced Confederate Army of Brigadier General P. G. T. Beauregard, whose forces were camped near Manassas Junction. McDowell's ambitious plan for a surprise flank attack on the Confederate left was poorly executed although the Confederates, who had been planning to attack the Union left flank, found themselves at an initial disadvantage.

Marine Corps Base Quantico (commonly abbreviated MCB Quantico) is a United States Marine Corps installation located near Triangle, Virginia, covering nearly 55,148 acres (86.169 sq mi; 22,318 ha; 223.18 km) of southern Prince William County, Virginia, northern Stafford County, and southeastern Fauquier County. Used primarily for training purposes, MCB Quantico is known as the "Crossroads of the Marine Corps".

Quantico Station is a census-designated place (CDP) in Prince William and Stafford counties in the U.S. state of Virginia, used by the Census Bureau to describe base housing. The population was 5,608 as of 2025.