The firm that was to become Sidley Austin was formed in Chicago in 1866 by Norman Williams and John Leverett Thompson as the partnership of Williams & Thompson . Among the firm 's first clients were the Pullman Company , the manufacturer of specialty sleeping railway cars , and former first lady Mary Todd Lincoln , then the widow of President Abraham Lincoln . Other early clients included Western Union Telegraph Company , which moved its Midwest headquarters from Cleveland to Chicago in 1869 . After the Great Chicago Fire of 1871 , the firm represented numerous insurance companies including Equitable Life Assurance Society . In 1892 , William Pratt Sidley joined the firm after having earned an LLB from Union College of Law and a M.A. from Harvard Law School . By 1913 , the firm 's name was changed to Holt , Cutting & Sidley , although Sidley would be the guiding personality for the Chicago firm through the 20th century . Three years later — the firm then fifty years old — had four partners , four clerks ( associates ) , and ten staff employees with gross income of around $ 100,000 ( roughly $ 1.9 million in 2008 dollars )
Great Chicago Fire
Great Chicago Fire
Sidley Austin