Fairfax County was named for Thomas Fairfax, sixth baron Fairfax of Cameron, proprietor of the Northern Neck. It was formed from Prince William County in 1742.

In seventeenth- and eighteenth-century Virginia, the term "tithable" referred to a person who paid (or for whom someone else paid) one of the taxes imposed by the General Assembly for the support of civil government in the colony. In colonial Virginia, a poll tax or capitation tax was assessed on free white males, African American slaves, and Native American servants (both male and female), all age sixteen or older. Owners and masters paid the taxes levied on their slaves and servants. For a more detailed history of tithables, consult the Library of Virginia's website for Colonial Tithables

Original wills and deeds as well as many other loose papers were destroyed during the Civil War; deed books for twenty-six of the fifty-six years between 1763 and 1819 are missing. Numerous pre-Civil War minute books are missing as well.