Marshalltown is a city in Marshall County, Iowa and is the county seat of the county. With a population of 27,591 at the 2020 census, it is the 1…Marshalltown is a city in Marshall County, Iowa and is the county seat of the county. With a population of 27,591 at the 2020 census, it is the 16th largest city in the state. Marshalltown is home to the Iowa Veterans Home and Marshalltown Community College.