Big Rock is an unincorporated community and census-designated place in Buchanan County, Virginia located at the convergence of County Route 650 and U.S. Route 460, a short distance from the Kentucky state line. It was first listed as a CDP in the 2020 census with a population of 199. A post office was established at Big Rock in 1854. The boulder from which the community likely took its name was destroyed in the 1930s by the building of the railroad.