FBI agents responded just before 3:20 p.m. to the U.S. Bank, located at 536 S. York St. in Elmhurst.
The suspect demanded money and pulled out a silver or gray handgun, the FBI said.
The individual fled on foot, and is currently at large.
SEE ALSO: FBI searching for suspect in 2 bank robberies at US Bank locations in Hanover Park, Schaumburg
Investigators said no one was hurt, but did not say if any money was stolen.
The suspect may be the same one involved in three other bank robberies, the FBI said.
Those took place Oct. 18, 2023 at the U.S. Bank, located at 60 S. Meacham Road in Schaumburg; Dec. 16, 2023 at the same Elmhurst U.S. Bank; and March 6 at the Schaumburg U.S. Bank.
The suspect is described as a 30- to 39-year-old man, who is about 6-feet tall. He has dark hair, possibly with a white patch or streak of blonde hair on the left side of his head. He has a medium-heavy build, and was last seen wearing a black-and-white patterned face mask, black zip-up jacket, baseball hat, blue jeans, athletic shoes and a gray or dark blue Under Armour backpack.
The public can report tips at 312-421-6700 and tips.fbi.gov.