Major Thomas Forsyth (December 5, 1771 – October 29, 1833) was a 19th-century American frontiersman and trader who served as a U.S. Indian agent to the Sauk and Fox during the 1820s and was replaced by Felix St. Vrain, prior to the Black Hawk War. His writings, both prior to and while an Indian agent, provided an invaluable source of the early Native American history in the Northwest Territory. His son, Robert Forsyth, was a colonel in the United States Army and an early settler of Chicago, Illinois.