The area around present-day Onawa was a stopping point in 1804 for Meriwether Lewis and William Clark during their exploration of the newly-obtained Louisiana Purchase. Many years later, that site was memorialized as the Lewis and Clark State Park. Monona County was formed in 1851. It was perhaps named for an Indian word meaning "beautiful valley." When Ashton was named the county seat in the fall of 1854, a log house served as the first courthouse. Ashton remained the county seat for only four years. That designation was moved to Onawa on April 5, 1858, and the first Monona County Courthouse was completed that same year.
Geography
According to the U.S. Census Bureau, the county has a total area of, of which is land and is water.
The 2010 census recorded a population of 9,243 in the county, with a population density of. There were 4,697 housing units, of which 4,050 were occupied.
2000 census
As of the census of 2000, there were 10,020 people, 4,211 households, and 2,737 families residing in the county. The population density was 14 people per square mile. There were 4,660 housing units at an average density of 7 per square mile. The racial makeup of the county was 98.34% White, 0.08% Black or African American, 0.76% Native American, 0.12% Asian, 0.04% Pacific Islander, 0.08% from other races, and 0.58% from two or more races. 0.70% of the population were Hispanic or Latino of any race. There were 4,211 households out of which 26.70% had children under the age of 18 living with them, 54.50% were married couplesliving together, 7.10% had a female householder with no husband present, and 35.00% were non-families. 31.00% of all households were made up of individuals and 17.50% had someone living alone who was 65 years of age or older. The average household size was 2.31 and the average family size was 2.88. In the county, the population was spread out with 23.20% under the age of 18, 6.20% from 18 to 24, 23.30% from 25 to 44, 23.30% from 45 to 64, and 23.90% who were 65 years of age or older. The median age was 43 years. For every 100 females there were 94.20 males. For every 100 females age 18 and over, there were 90.50 males. The median income for a household in the county was $33,235, and the median income for a family was $41,172. Males had a median income of $27,349 versus $19,607 for females. The per capita income for the county was $17,477. About 6.60% of families and 9.40% of the population were below the poverty line, including 8.90% of those under age 18 and 9.50% of those age 65 or over.
