Sullivan County is a county located in the northern portion of the U.S. state of Missouri. As of the 2010 census, the population was 6,714. Its county seat is Milan. The county was organized February 14, 1845 and named for Major General John Sullivan of the American Revolutionary War.HistoryIn 1682, René-Robert Cavelier, Sieur de la Salle claimed the territory west of the Mississippi River for France, which included present-day Sullivan County. The United States acquired this region under terms of the Louisiana Purchase on July 4, 1803. Twenty-one years later, the Sac (Sauk), Meskwaki (Fox), and Iowa Native American nations ceded their tribal land to the U.S. government under two treaties in August 1824.Dr. Jacob Holland and his son, Robert W. Holland, arrived in 1836, becoming the county's first permanent White settlers. Dr. Holland, a veteran of the Black Hawk War and practitioner of herbal medicine, and son staked their home sites at the Main Locust Creek Settlement near a place called Scottsville. American pioneers from Ohio, Illinois, Kentucky, Tennessee, and Virginia quickly followed them and established farms and small businesses at Pharsalia (Milan) Settlement, Yellow Creek Settlement, and Jackson's Corners (Jacksonville) by 1840.
