Mason City is a city in Mason County, Illinois, United States. The population was 2,343 at the 2010 census, and 2,155 at a 2018 estimate. Mason City was established in 1857.
The city took its name from Mason County.
Mason City is located at 40°12′11″N 89°41′46″W (40.202965, -89.696109).
According to the 2010 census, Mason City has a total area of 1.01 square miles (2.62 km2), all land.
Mason City is situated halfway between Peoria and Springfield on Route 29, a north-south highway, and halfway between Lincoln and Havana on Route 10, an east-west road.
At the 2000 census, there were 2,558 people, 1,041 households and 681 families residing in the city. The population density was 2,599.1 per square mile (1,007.8/km2). There were 1,127 housing units at an average density of 1,145.1 per square mile (444.0/km2). The racial makeup of the city was 99.06% White, 0.04% African American, 0.08% Native American, 0.16% Asian, 0.27% from other races, and 0.39% from two or more races. Hispanic or Latino of any race were 0.59% of the population.
There were 1,041 households, of which 30.4% had children under the age of 18 living with them, 51.3% were married couples living together, 11.2% had a female householder with no husband present, and 34.5% were non-families.