Saline County is a county located along the Missouri River in the U.S. state of Missouri. As of the 2010 census, the population was 23,370. Its county seat is Marshall. The county was established November 25, 1820, and named for the region's salt springs.Settled primarily by migrants from the Upper South during the nineteenth century, this county was in the region bordering the Missouri River known as "Little Dixie". In the antebellum years it had plantations supported by enslaved workers.