Sidley Austin LLP, formerly known as Sidley Austin Brown & Wood LLP, is one of the oldest law firms in the world. It is the sixth-largest U.S.-based corporate law firm with over 1,800 lawyers, annual revenues of more than one billion dollars, and offices in 16 cities worldwide, with the most recent addition of Sydney, Australia, in May 2007. It is a full-service law firm, with broad experience in transaction and litigation matters. Its original predecessor firm was founded in 1866 and had Mary Todd Lincoln, the widow of President Abraham Lincoln, among its earliest clients. The firm was formed as the result of the merger of two firms: the Chicago-based Sidley & Austin, founded in 1866, and the New York-based Brown & Wood, founded in 1914. The merger was completed in May 2001.
As of 2006, it was the 9th largest law firm in the world (and 5th in the US) by revenue.
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. One of the nascent firm's first clients was the Pullman Company, the manufacturer of specialty sleeping railway cars. 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 the late 1800s, Williams & Thompson counseled several utility and railroad companies expanding in the West, incluidley joined the firm after having earned an LLB from Union College of Law and a further 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 50 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).