Marysville is a city in Marion County, Iowa, United States. The population was 44 at the time of the 2020 census. Marysville is located on the n…Marysville is a city in Marion County, Iowa, United States. The population was 44 at the time of the 2020 census. Marysville is located on the north bank of Cedar Creek, 15 miles southeast of Knoxville, the county seat of Marion County.