O'Leary's was founded in 1949 by John J. O'Leary Sr. and his wife Ruth in a one-room office located on Lake Street in Chicago. Since the 1960's, the company had been operating at 4554 West North Avenue until 2011 when John Jr. acquired a new, spacious facility on North Cicero Avenue. Over the years, the company has continued to flourish. Prior to opening O'Leary's, John Sr. worked as an Operating Engineer and as a salesman for the Thor Construction Tool Company. His sales territory was the Chicagoland area where he was laying the ground work for his future company. He passed away in 1978 and Ruth ran the business until John Jr. took over in 1991. "We are always keeping with the times by updating and modernizing our equipment and procedures," said John J. O'Leary, Jr.