Police say it happened around 3 p.m. at the Bull Dog Federal Credit Union on 17555 York Road.
Police say the suspect entered the bank and displayed a hand gun. They say the suspect fled the scene with an undisclosed amount of money.
The suspect is described as a white male wearing dark clothing.
The Washington County Sheriff's Office along with the Hagerstown State Police is asking anyone with information in this incident to call them at (240)-313-2195.