Mason City is a city in Mason County, Illinois, United States. The population was 2,558 at the 2000 census, and 2,324 at a 2009 estimate. Mason City was established in 1857.
Mason City is located at 40°12′11″N 89°41′46″W / 40.20306°N 89.69611°W / 40.20306; -89.69611 (40.202965, -89.696109).
According to the 2010 census, Mason City has a total area of 1.01 square miles (2.62 km), 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. 31.5% of all households were made up of individuals and 18.3% had someone living alone who was 65 years of age or older. The average household size was 2.38 and the average family size was 2.95.
Age distribution was 25.2% under the age of 18, 7.0% from 18 to 24, 25.3% from 25 to 44, 20.7% from 45 to 64, and 21.9% who were 65 years of age or older. The median age was 40 years. For every 100 females, there were 87.1 males. For every 100 females age 18 and over, there were 81.7 males.
The median household income was $35,615, and the median family income was $47,991. Males had a median income of $35,058 versus $21,875 for females. The per capita income for the city was $18,411. About 6.8% of families and 9.3% of the population were below the poverty line, including 13.6% of those under age 18 and 8.0% of those age 65 or over.