McDuffie County Sheriff Logan Marshall said no one was injured during the robbery that happened shortly before 10 p.m.
The robber was described only as a black man, who got away with an undisclosed amount of money, Marshall said.
Video surveillance was being examined by authorities.
"We're hopeful that we can develop a picture and get that out so the public might be able to help us," said Mike Ayers, special agent in-charge of the Georgia Bureau of Investigation Region 7 Office in Thomson.
Marshall said he requested the GBI's assistance and that the case is jointly being investigated.