It happened on Monday around 1:30 p.m. at the branch on Lincoln Avenue.
The FBI said the man walked into the bank with a note demanding money. No one was hurt.
The suspect, described as between 30 and 39 years old and about 5-foot-8, wore a black beanie-style hat, dark-framed sunglasses, two surgical masks, black sweatpants, blue loafers or slippers and a loose-fitting, long-sleeved, dark-colored jacket with a full zipper, the FBI said. The jacket covers a gray sweatshirt, which covers a black shirt. He also had a dark-colored beard.
Officials asked anyone who recognizes him to call the FBI or Lincolnwood police.
The FBI said the public can report tips at 312-421-6700 and tips.fbi.gov.