The grant became actual in 1660 when Charles was restored to the English throne. By 1719, these lands had been inherited by Thomas Fairfax, 6th Lord Fairfax of Cameron (1693-1781). By that time the question of the boundaries of the designated lands had also become highly contentious. It was decided in 1746 that a line between the sources of the North Branch of the Potomac and the Rappahannock River (the "Fairfax Line") would constitute the western limit of Lord Fairfax's lands.
The unsettled portions of his domain were finally confiscated during the American Revolution by the Virginia Act of 1779 and when he died in 1781 the Proprietary effectively ceased to exist. A portion of this estate, however, was later the subject of the landmark Supreme Court case Martin v. Hunter's Lessee (1816).
In September 1649, King Charles II of England granted to seven Englishmen all of Virginia between the Rappahannock and Potomac Rivers as a Proprietary. The extent of the grant was hardly recognized by either the King or the grantees because most of it had never even been mapped. The proprietors thought little of their grant since Charles II, due to political struggles in England, was a king without a kingdom.
In the mid seventeenth century, control of the Proprietary had come to one man, Thomas Colepeper, 2nd Baron Colepeper who also received a new patent issued by King James II in 1688. Lord Colepeper died the following year. His 5/6th share of the proprietary was inherited by his daughter Catherine Culpeper and her husband Thomas Fairfax, 5th Lord Fairfax of Cameron. While some of the original proprietors' rights had been lost, the collecting of taxes from settlers had been established through the efforts of their agents in Virginia and through Lord Fairfax himself to ensure that the proprietors received their income from their property. After Lord Fairfax died in January 1710, his son Thomas, the 6th Lord, inherited the title and his five-sixths shares in the Northern Neck. In May, his grandmother died leaving the new Lord Fairfax her one-sixth share. Because he was only sixteen years old at the time, the affairs of the Proprietary fell to his mother, Lady Catherine Fairfax. When she died in 1719, the sixth Lord Fairfax came to control all six shares of the proprietary.
As the Virginia government at Jamestown were losing control over a significant portion of Virginia held by Lord Fairfax, the feud between them was significant. The specific issue at this time was the southern and western boundaries of the proprietary. In 1735 Lord Fairfax came to Virginia to see about a survey to settle the matter. The survey was undertaken in 1736 (see Fairfax Stone) and the next year Fairfax returned to England to argue his case before the Privy Council. Before leaving, he rode over much of his domain, and set aside for himself a tract of 12,588 acres (50.94 km2) near Great Falls, in what was to become Fairfax County. A second survey was conducted with great difficulty in 1746 (the Fairfax Line) setting a line between the sources of the Potomac and Rappahannock.
In 1747, Lord Fairfax came back to Virginia, two years after having won his claim before the Privy Council to the most extensive boundaries for the proprietary in exchange for certain land concessions to the Virginia authorities. Virginia had won political control over the proprietary and its inhabitants in the seventeenth century. When Lord Fairfax died in 1781 in Virginia, the proprietary effectively ceased to exist. All the land which had been granted by Lord Fairfax remained in the hands of the grantees; the remainder of ungranted land came under the control of the new Commonwealth of Virginia.
Prior to 1649, the entire Northern Neck had been designated by the Assembly as one large county called Northumberland. In 1653, the majority of the northern portion of Northumberland was named Westmoreland County. In 1664, Stafford County was created from the northern portion of Westmoreland. What is now Fairfax was first in Northumberland, then Westmoreland, and from 1664 to 1730, Stafford.