Mason City is a city in Cerro Gordo County, Iowa, United States. The population was 29,172 at the 2000 census. It is the county seat of Cerro Gordo County^GR6. North Iowa Area Community College is located here.

Mason City is the birthplace and childhood home of composer and playwright Meredith Willson. The fictional city of River City, Iowa in his musical The Music Man is loosely based on Mason City. Willson's birthplace has been restored as a tourist attraction and is part of the Music Man Square complex that includes a plaza with a bronze statue of Willson in a band major's uniform. Puppeteer Bil Baird was also born in Mason City; his creations were featured in The Sound of Music and are now exhibited at the MacNider Art Museum. After a concert at the Surf Ballroom in nearby Clear Lake, IA, Buddy Holly, Richie Valens and the Big Bopper died in a plane crash after taking off from the Mason City airport.

Mason City is also known for its sizable amount of Prairie School architecture, presumed to be the largest concentration in one location anywhere in the world. The Rock Glen and Rock Crest districts along Willow Creek feature homes designed by Frank Lloyd Wright and Walter Burley Griffin. Wright's Stockman House has been restored and is open to the public. Also, Wright's Park Inn Hotel, the only remaining hotel in the world designed by him still standing, is in the process of being restored.

Mason City is home to the Iowa Traction Railroad. The IATR is one of the last surviving electric interurban railroads in the U. S., and the only one that still uses electric locomotives to haul freight in regular service.

The largest employer is Mercy Medical Center-North Iowa. Other major industry includes door manufacturer Curries/Graham Company and the Kraft Foods plant that produces the nation's entire supply of refrigerated ready-to-eat Jell-O gelatin and Jell-O pudding snacks. Mason City is also a major production center for Portland cement.