"Lydia ADAIR, b.1779 Hawkins Co., TN, d. 1838 Madison Co., AL mc. 1795 Hawkins Co TN to (Rev.) William BYRD (a Baptist Minister ?) b: 1775 Fincastle, Botetourt Co VA, d. 21 March 1856 Franklin Co AL"
This may refer to the TOWN of Fincastle, County seat of Botetourt County.It was not part of Fincastle County, which was created from part of Botetourt in 1772, and divided into Montgomery, Washington, and Kentucky Counties in 1776.The town of Fincastle remained (and still remains) in Botetourt County this entire time.
This website is good for visualizing the former and present county boundaries.