Plymouth is a city in Cerro Gordo County, Iowa, United States, along the Shell Rock River.

[2] It is part of the Mason City Micropolitan Statistical Area.

[3] According to the United States Census Bureau, the city has a total area of 0.44 square miles (1.14 km2), all land.

There were 179 housing units at an average density of 405.6 per square mile (156.6/km2).

There were 180 housing units at an average density of 409.1 per square mile (158.0/km2).

27.4% of all households were made up of individuals, and 7.3% had someone living alone who was 65 years of age or older.

There were 171 housing units at an average density of 389.3 per square mile (150.3/km2).

The racial makeup of the city was 98.83% White, 0.70% Native American, and 0.47% from two or more races.

22.0% of all households were made up of individuals, and 11.6% had someone living alone who was 65 years of age or older.