Marysville is a city in St. Clair County of the U.S. state of Michigan. The population was 9,959 at the 2010 census. The municipality was founded in 1919, first as a village, then became a city in 1924.Marysville is located on the western shore of the St. Clair River, across from Corunna, Ontario. The city is marked by winding streets, subdivisions, a riverfront boardwalk, and an industrial park. The city was home to the former Wills Sainte Claire Automotive company, a Morton Salt plant, and Detroit Edison's Marysville Power Plant.