Keokuk County was formed in 1837. It was named for the eponymous chief of the Sac Indians, who advocated peace with the white settlers. In May 1843, the county opened for public settlement and was self-governed from 1844. Previously it was governed by Washington County. After a debate lasting a few years for the location for the county seat, the right went to Sigourney in 1856. Keokuk County is unusual in that it has two county fairs. The Keokuk County Fair is held in What Cheer and immediately followed by the Keokuk County Expo which is held in Sigourney.
As of the census of 2000, there were 11,400 people, 4,586 households, and 3,155 families residing in the county. The population density was 20 people per square mile (8/km²). There were 5,013 housing units at an average density of 9 per square mile (3/km²). The racial makeup of the county was 99.00% White, 0.07% Black or African American, 0.11% Native American, 0.23% Asian, 0.02% Pacific Islander, 0.21% from other races, and 0.36% from two or more races. 0.54% of the population were Hispanic or Latino of any race.
There were 4,586 households out of which 30.50% had children under the age of 18 living with them, 59.00% were married couples living together, 6.50% had a female householder with no husband present, and 31.20% were non-families. 27.80% of all households were made up of individuals and 15.80% had someone living alone who was 65 years of age or older. The average household size was 2.45 and the average family size was 2.99.
In the county the population was spread out with 25.70% under the age of 18, 7.00% from 18 to 24, 25.50% from 25 to 44, 21.60% from 45 to 64, and 20.20% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 94.10 males. For every 100 females age 18 and over, there were 91.80 males.
The median income for a household in the county was $34,025, and the median income for a family was $41,818. Males had a median income of $28,306 versus $22,083 for females. The per capita income for the county was $17,120. About 7.50% of families and 10.10% of the population were below the poverty line, including 12.90% of those under age 18 and 10.50% of those age 65 or over.