Mason City, IA has a population of 27,546 and is the 1,560th largest city in the United States. The population density is 991 per sq mi which is 1714% higher than the Iowa average and 994% higher than the national average. The median age in Mason City is 43 which is approximately 12% higher than the Iowa average of 38. In Mason City, 53% of the population over 15 years of age are married, 96% speak English and 2% speak Spanish. 76% of Mason City residents were born in Iowa, 21% were born out of state, 0% were born outside of the United States and 3% were foreign born.