Mason City, IL has a population of 2,272 and is the 10,333rd largest city in the United States. The population density is 2,242 per sq mi which is 908% higher than the Illinois average and 2374% higher than the national average. The median age in Mason City is 45 which is approximately 20% higher than the Illinois average of 37. In Mason City, 60% of the population over 15 years of age are married, 100% speak English and 0% speak Spanish. 85% of Mason City residents were born in Illinois, 14% were born out of state, 0% were born outside of the United States and 0% were foreign born.