The robbery happened at 10:06 a.m. on Monday at the PNC Bank inside the Giant food store at 2450 Chemical Road.
Police say the man handed a demand note to the teller and left on foot, possibly carrying a white plastic Giant supermarket bag.
The man is described as a white male standing about 5'10" tall and weighing approximately 160 pounds. He appeared to be in his 20s and had a noticeable black eye.
He was wearing a gray hooded sweatshirt and white sunglasses.
Anyone with information is asked to contact the Plymouth Township Police Detective Division at 610-279-1901.