b. February 22, 1794, in Paris, Kentucky; d. January 15, 1844, in Jacksonville, Illinois. Duncan fought with the Seventeenth United States Infantry during the War of 1812. In 1818, he moved from Kentucky to Illinois and gradually acquired tracts of land throughout the state. In 1824, Duncan was elected as a state representative from Jackson County. Two years later, he was elected to the United States House of Representatives and served until 1834. As a Congressman, Duncan advocated the immediate sale of public land in Illinois and surrounding states and territories, and he argued that the revenue generated from such sales of land should be given to the states for the purpose of internal improvements and education. In 1834, Duncan was elected governor of Illinois, and the Whig party supported him, although party lines had yet to be clearly drawn. He supported the construction of the Illinois and Michigan Canal, but as a general rule, he believed that internal improvements within a state should be left to private initiative. Duncan served as governor until 1838. He ran for governor in 1842, but was defeated.