Mason City is the county seat of Cerro Gordo County, Iowa, United States. The population was 28,079 in the 2010 census, a decline from 29,172 in the 2000 census. The Mason City Micropolitan Statistical Area includes all of Cerro Gordo and Worth counties. It is commonly referred to as the "River City", as the city grew up centered on the Winnebago River.
The region around what would later be first called Shibboleth was a summer home to the Sioux and Winnebago nations. The first settlement that became Shibboleth was established in 1853 at the confluence of the Winnebago River and Calmus Creek. The town had several names: Shibboleth, Masonic Grove, and Masonville until Mason City was adopted in 1855, in honor of a founder's son, Mason Long.
In 1854, John McMillin opened the first store, and Dr. Silas Card opened the first medical practice in the area. Lizzie Thompson established the first schoolhouse in a log cabin in 1856. The United States Post Office Department started service to the town in 1857.