Namesake. Fairfax County and Fairfax City are named after Thomas Fairfax, Sixth Baron of Cameron (1693-1781). History buffs will know that Thomas was a favorite family name Thomas, 3rd Baron, played a major role in English history as an associate of Cromwell. Thomas Fairfax inherited large estates in Northern Virginia and moved here permanently about 1746. It was his cousin William Fairfax who built Belvoir, his family home, on the promontory that is now Fort Belvoir. Belvoir of course refers to the beautiful view of the river.