First called Highland, Sullivan County was formed, 1843. Fully organized in 1845, it was named for Revolutionary War Gen. John Sullivan. Comprising 654 sq. miles of high glacial prairie land, the county lies in territory ceded 1824, by Iowa, Sac and Fox tribes. Massive boulders left by the glacier, and many Indian mounds remain in the area. First settlers were Dr. Jacob Holland and his son, R.W. Holland, in 1836.Milan, the county seat, where an Indian mound was leveled to form the public square, was laid out 1845, on land given by A.C.Hill and bought from Hiram Phillips. Last U.S. Land Office established in Mo., was located there 1849-59. During the Civil War, a Union post was maintained at Milan and guerrilla bands raided the county.Railroad development in 1870's brought modern growth to the county. Milan grew as shipping center and railroad division point when the C., B., & K.C. (now C. B. & Q.), east and west, 1871-1881.The C., M., & St.P., was built in west part of the county in 1886. Side 2
Rich grain fields and productive dairy, livestock and poultry farms characterize Sullivan County. The main watercourses are Medicine, Locust, East Locust, Yellow and Spring creeks. Early pioneers were from VA., KY., Tenn., Ohio, and Ill. Among county towns are Green Castle, laid
Side 2out, 1857; Newton, 1858; Pollock, 1873; Boyton and Core, 1877; Winigan and Green City, 1880; Humphreys and Reger, 1881; and Osgood, 1886: and Harris, 1887. Among early schools were Green City College, opened in 1885, and Humphreys College and Business Institute in 1884. In the 1880's, Reger was an important railroad tie shipping point.Near Osgood and west of Milan, is the widely-known Camp Ground and pioneer cemetery. There in the 1850's, at the site of an early wagon-trail camping ground, the Methodist Episcopal Church South and the Cumberland Presbyterian Church organized Camp Meeting Grounds. Congregations from all over the county held meetings there until the Civil War when all installations were burned. Today's interdenominational church building there was built in 1901.