[1] O'Leary was born at 137 DeKoven Street, the house in which his family lived and where the Great Chicago Fire would start two years later.
O'Leary worked for the local bookies when he was a teenager, and eventually, he began as a bookmaker himself in Long Beach, Indiana, an off-track betting resort.
In the early 1890s, he left the Stock Yards and opened a saloon on Halsted Street which included Victorian Turkish baths, a restaurant, a billiard room, and a bowling alley.
O'Leary refused to bribe the police and instead had his saloon protected by adding a set of iron and zinc layered oak doors which allegedly were "fireproof, bomb-proof, and police-proof".
The perception was that O'Leary, along with gambling bosses Mont Tennes and "Hot Stove" Jimmy Quinn, controlled the Chicago Police.