The Will County Sheriff's Office said deputies were called to the bank on South Harlem at 11:40 a.m.
The robbers threatened tellers with guns. There were "numerous" customers at the bank at the time.
One of the robbers went with an employee to the vault. The robber hit that employee on the head with a pistol.
The suspects got away in a dark blue Dodge Challenger.
Anyone with information is asked to contact Detective Danielle Strohm with the Will County Sheriff’s Office at 815-727-8574, at extension 4930.