Following the 1722 Treaty of Albany, in which the Iroquois abandoned all lands east of the Blue Ridge Mountains to the colony of Virginia, colonists and new immigrants of a wide variety of ethnic and religious backgrounds began settling the lands that would become Loudoun County. In 1730, Thomas, the 6th Earl of Fairfax, granted 4,054 acres, including what would become Leesburg, to Francis Awbrey. At the intersection of the major north-south Carolina Road (now U.S. Highway 15) and the east-west oriented Potomac Ridge Road (now Virginia Highway 7), a small settlement emerged.
In 1757 the Assembly of Virginia selected this settlement for the location of the Loudoun County courthouse. The land was then owned by Nicholas Minor, who hired John Hough to survey and plat his 60 acres into 70 lots to form a town, which he called George Town. The name was changed to Leesburg the following year, in honor of the Lee family. In September 1758, an Act of the Assembly established the Town of Leesburg, although the town was not incorporated until 1813.
The pace of change in Leesburg and Loudoun County accelerated after the end of the Second World War. With the end of war-time restrictions on fuel and rubber, and new with government programs like the GI bill, which enabled returning veterans to pursue higher education opportunities previously out of reach, a life dominated by the cycles of agriculture was challenged.
Leesburg experienced growing pains as the population grew and Leesburg became increasingly integrated into the greater Washington area. Nonetheless, many residents advocated measures to retain Leesburg's historic character. The civil rights era further changed the town, although racial integration in Leesburg was not marked by the violence seen in some southern towns: high schools began desegregating in 1962 and were fully integrated by 1968.
Leesburg was also home to General George C. Marshall, Secretary of State and architect of the plan to rebuild devastated Europe after the Second World War, and Arthur Godfrey, a national radio and television personality who was also a Leesburg aviator and philanthropist.