Fairfax Stone Historical Monument State Park is a West Virginia state park commemorating the Fairfax Stone, a surveyor's marker and boundary stone at the source of the North Branch of the Potomac River in West Virginia. The original stone was placed on October 23, 1746 to settle a boundary dispute between Thomas Fairfax, 6th Lord Fairfax of Cameron and the English Privy Council concerning the Northern Neck of Virginia. It determined the proprietorship and boundaries of a large tract of mostly unsurveyed land in the English colonies of Maryland and Virginia.