Former county of colonial Virginia, created in 1772 and extending westwards into territory which included much of present-day Kentucky.

Fincastle County was created from Botetourt County as settlement and surveying moved further west. William Preston served as county surveyor. Under Virginia law, surveys intended to establish legal title had to be carried out by the official county surveyor or by deputies appointed under his authority.

The county consequently appears frequently in the surviving records of western land claims. In 1773 Hancock Taylor, a deputy surveyor, was already working in Kentucky. John Floyd was appointed deputy surveyor on 2 March 1774, and William Russell on 2 August. Their surveys were entered in the Fincastle County books and later formed the basis of numerous Kentucky land titles.

In January 1775 the freeholders of Fincastle produced one of the strongest colonial declarations of resistance to Parliamentary authority. The committee which prepared the resolutions was chaired by William Christian, brother-in-law of Patrick Henry.

The address declared that the settlers would never surrender their liberties "to any power on earth, but at the expense of our lives" and condemned the extension of "the hand of unlimited power" over the colonies. The Fincastle address was dated 20 January 1775.

Fincastle County was short-lived. Its records nevertheless preserve a large part of the early documentary history of western Virginia and Kentucky immediately before the American Revolution.