Employees told police a hooded, masked man vaulted the counter and then emptied one of the cash drawers.
The man stole an undetermined amount of money and fled, running south on Main Street.
The reward is being offered by the Connecticut Banker’s Association.
The suspect is described as heavyset, at least 6 feet tall, wearing an all gray sweat suit with the hooded sweatshirt pulled tight around his face, a surgical style mask and clear latex gloves, Mikulski said. No weapon was shown.
Anyone with information is asked to call police at (203) 294-2805.