Fairfax County was created in 1742 from Prince William County. The name Fairfax was adopted from Thomas, sixth Lord Fairfax, Baron of Cameron.

In 1649 the exiled English King Charles II granted a huge area of land between the Potomac and Rappahannock Rivers, known as the Northern Neck, to eight of his most loyal supporters. By 1681, one of those men, Thomas, Lord Culpeper, and Governor of the Virginia Colony, had acquired the interests of the others. When Lord Culpeper died in 1689 his vast land holdings of approximately 5 million acres passed to his only daughter Catherine. Catherine married Thomas, fifth Lord Fairfax. On their deaths the lands passed to their son, Thomas, sixth Lord Fairfax.

Thomas, sixth Lord Fairfax was the only Fairfax to actually reside on the Fairfax Land Grant. In 1735 he arrived in Virginia to personally survey his land holdings. Two years later, he returned to England until 1747. Upon his return to Virginia, he lived at Belvoir along the Potomac River in present day Fairfax County and later moved to an estate, Greenway Court, in present day Clarke County, Virginia.

While at Belvoir, Lord Fairfax made the acquaintance of a young man named George Washington whose family resided just five miles away at Mount Vernon. Lord Fairfax was sufficiently impressed with George that he employed him to survey his lands in the Shennandoah Valley. Surveyors were among the most prosperous professionals of the day. A surveyor could earn an income at least equal to the best trial lawyers in the colony. In addition many surveyors acquired large estates of the best lands because of their intimate knowledge of the country. Consequently, his association with the Fairfax family heavily influenced his fortunes and the course of our country.