Marshall is a city in Saline County, Missouri, United States. The population was 13,806 at the 2020 census. It is the county seat of Saline County…Marshall is a city in Saline County, Missouri, United States. The population was 13,806 at the 2020 census. It is the county seat of Saline County. The Marshall Micropolitan Statistical Area consists of Saline County. It is home to Missouri Valley College.