Alleghany County was named for the Allegheny Mountains, although it has a variant spelling. It was formed from Bath, Botetourt, and Monroe (West Virginia) Counties in 1822, and additional parts of Bath (1823) and Monroe (1843) were added. It area is 444 square miles, and the county seat is Covington. The former independent city of Clifton Forge reverted to the county in 2001.

First known as commissions, the first Justice of the Peace office originated with the county quarterly court in 1623. Commanders of Plantations (1607-1629) were predecessors of the commissioners, who since 1662 have been called justices of the peace. They have traditionally had both civil and criminal jurisdiction, and have served other functions, including performing coroners' and lunacy inquisitions. Until 1869 justices served both as judges of the county court and as individual justices, since then they have had only the latter function.