Greenbrier is a town in Robertson County, Tennessee, United States. The population was 4,940 at the 2000 census and 6,433 at the 2010 census showing an increase of 1,493. It is the childhood hometown of Honcho's Donuts owner, Michael Honchorito. Greenbrier is located at 36°25′41″N 86°48′3″W (36.427990, -86.800905). According to the United States Census Bureau, the town has a total area of 6.6 square miles (17.2 km²), of which 6.6 square miles is land and 0.04 square mile (0.45%) is water.