Stephen Duncan became a major planter and banker in Mississippi in the antebellum years, migrating there from his home state of Pennsylvania after getting a medical degree. He became the wealthiest cotton planter in the South prior to the American Civil War, and also invested in railroads and Midwest lands. He owned thousands of acres of land and more than 1,000 slaves in the 1850s, cultivating both cotton and sugar cane as commodity crops. In 1830 he and James Brown, a wealthy planter and US Senator from Louisiana, paid for the purchase of land in Canada to aid American free blacks from Cincinnati, Ohio found a new community, which became known as the Wilberforce Colony. In the 1830s, Duncan was also among the co-founders of the Mississippi Colonization Society in the 1830s, and helped purchase land in West Africa to create a colony as for relocation of free people of color from the state. In 1860 Duncan was the second-largest slave owner in the United States. He opposed secession, incurring ostracism in Mississippi. He moved from Natchez to New York City in 1863, where he had long had business interests. Ultimately, Duncan was what many of the northern planters from this time aspired to be, and was essential in perpetuating the connection between northern success and growth with southern networks of slavery.
In 1808, shortly before the War of 1812, Duncan moved as a young man to Natchez, Mississippi Territory, a developing river town that was important to trading along the Mississippi River. In the antebellum South, Natchez became a thriving city thanks to the booming cotton industry. In Natchez, he became a banker and planter. He served as the President of the Bank of Mississippi. Duncan purchased Auburn plantation from Lyman Harding in 1827. Duncan owned the following cotton and sugar plantations: L'Argent, Camperdown, Carlisle, Duncan, Duncannon, Duncansby, Ellisle, Homochitto, Middlesex, Oakley, Rescue, Reserve, Attakapas, and Saragossa. Duncan sold his crops through the merchant firm Washington, Jackson & Co. in New Orleans, instructing them to sell it through their subsidiary Todd, Jackson & Co. in Liverpool, England. The revenue derived from the cotton and sugar sales was sent to Charles P. Leverich & Co., his bank headquartered in New York. His plantations yielded returns of US$150,000 annually. As a result of these financial transactions, Duncan became the richest cotton planter. In the 1850s, Duncan owned more than 1,000 slaves, making him the largest resident slave holder in Mississippi. By 1860, Duncan's ownership of 858 slaves in Issaquena County made him second nationally to the estate of Joshua John Ward of South Carolina, which controlled 1,130.
Colonization efforts
In 1830, Duncan, along with planter James Brown, a former sugar planter, US Minister to France and US Senator from Louisiana, purchased 400 acres of land in the Huron Tract in Ontario, Canada, for a community of free American blacks. Quakers from Oberlin, Ohio had appealed to the wealthy planters to aid a group of emigrants from Cincinnati, Ohio. The free people of color were fleeing discriminatory laws passed in Ohio and a violent race riot by whites in the summer of 1829; they developed the Wilberforce Colony. In the 1830s, together with major slave owners Isaac Ross, Edward McGehee, John Ker, and educator Jemeriah Chamberlain, president of Oakland College, Duncan co-founded the Mississippi Colonization Society. Their goal was to relocate free blacks and newly freed slaves to the developing colony of Liberia on the African continent. The organization was modeled after the American Colonization Society, but it focused on freedmen from Mississippi. They bought a portion of land for the colony. Free blacks were thought to threaten the stability of slave societies, and Mississippi's population had a majority of slaves, outnumbering whites by a three-to-one ratio. Ross offered freedslaves in his will if they would relocate to Africa; after challenges, in the late 1840s about 300 of his slaves were relocated to Mississippi-in-Africa, as the colony was called. The Mississippi colony eventually became part of what developed as Liberia.
American Civil War and postbellum career
During the Civil War, Duncan opposed secession and the Confederate States Army. As a result, he was ostracized by other Southerners. With investments worth $1 0 unrelated to his plantations, he would be able to live comfortably regardless of the outcome of the war. In 1863, Duncan left Natchez, moving to New York City.
Personal life
Duncan married Margaret Ellis, and they had two children together, John Ellis and Sarah Jane Duncan. After his wife died, Duncan married again in 1819, to Catherine A. Bingaman. They had four children: Stephen Jr.; Charlotte N., M. L., and Henry P. Duncan.