Plymouth is a city in Cerro Gordo County, Iowa, United States, along the Shell Rock River. The population was 429 at the 2000 census. It is part of the Mason City Micropolitan Statistical Area.
Plymouth is located at 43°14′43″N 93°7′21″W / 43.24528°N 93.1225°W / 43.24528; -93.1225 (43.245346, -93.122575).
According to the United States Census Bureau, the city has a total area of 0.4 square miles (1.1 km²), all of it land.