Founded in Chicago by W. Clement Stone, this company would become the nation's largest door-to-door accident and health insurance company. Stone, who worked with his mother in the insurance business when he was still a teenager, opened his own small agency, the Combined Registry Co., in Chicago in 1922. Twenty-five years later, after his business had expanded considerably, Stone created the Combined Insurance Co. of America. By the beginning of the 1960s, Combined Insurance employed about 1,500 people and collected nearly $100 million in annual premiums. During the final decades of the twentieth century, Stone's company continued to expand, particularly after merging with the Ryan Insurance Group in 1982. By 1987, when Combined Insurance changed its name to Aon Corp., annual revenues stood at roughly $2.5 billion. The number of Chicago-area residents employed by the company rose from 1,500 in the mid-1970s to about 6,000 by the end of the 1990s. In 2002, Aon was a large international corporation with over 55,000 employees in 600 offices in 125 countries around the world.

This entry is part of the Encyclopedia's Dictionary of Leading Chicago Businesses (1820-2000) that was prepared by Mark R. Wilson, with additional contributions from Stephen R. Porter and Janice L. Reiff.