Cerro Gordo County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 43,127. Its county seat is Mason City. The county is named for the Battle of Cerro Gordo, which took place during the Mexican–American War.

Mason City is a city and the county seat of Cerro Gordo County, Iowa, United States. The population was 27,338 in the 2020 census. Mason City is known for its musical heritage, high concentrations of renowned Prairie School style architecture, and a close connection with nearby resort town Clear Lake.