- Peter Gusenberg, a frontline enforcer for the Moran organization.
- Frank Gusenberg, the brother of Peter Gusenberg and also an enforcer. Frank was still alive when police first arrived on the scene, despite reportedly having fourteen bullets in his body. When questioned by the police about the shooting his only response was "nobody shot me". He died three hours later.
- Albert Kachellek (alias "James Clark"), Moran's second-in-command, a retired man at the time, he was not a member of the gang himself but happened to be there at the time the killing happened.
- Adam Heyer, the bookkeeper and business manager of the Moran gang.
- Reinhart Schwimmer, an optician who had abandoned his practice to gamble on horse racing (unsuccessfully) and associate with the Moran gang. Though Schwimmer called himself an "optometrist" he was actually an optician (an eyeglass fitter) and he had no medical training.
- Albert Weinshank, who managed several cleaning and dyeing operations for Moran. His resemblance to Moran, including the clothes he was wearing, is what allegedly set the massacre in motion before Moran actually arrived.
- John May, an occasional car mechanic for the Moran gang, though not a gang member himself. May had had two earlier arrests (no convictions) but was attempting to work legally. However, his desperate need of cash, with a wife and seven children, caused him to accept jobs with the Moran gang as a mechanic.