Henderson County is part of the Burlington, IA–IL Micropolitan Statistical Area.
As of the census of 2000, there were 8,213 people, 3,365 households, and 2,375 families residing in the county. The population density was 22 people per square mile (8/km²). There were 4,126 housing units at an average density of 11 per square mile (4/km²). The racial makeup of the county was 98.50% White, 0.26% Black or African American, 0.11% Native American, 0.10% Asian, 0.04% Pacific Islander, 0.18% from other races, and 0.82% from two or more races. 0.88% of the population were Hispanic or Latino of any race. 24.7% were of German, 23.5% American, 13.2% English, 13.2% Irish and 6.0% Swedish ancestry according to Census 2000. 98.2% spoke English and 1.4% Spanish as their first language.
There were 3,365 households out of which 28.60% had children under the age of 18 living with them, 59.60% were married couples living together, 7.10% had a female householder with no husband present, and 29.40% were non-families. 25.30% of all households were made up of individuals and 12.40% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.88.
In the county the population was spread out with 23.10% under the age of 18, 7.50% from 18 to 24, 26.20% from 25 to 44, 26.50% from 45 to 64, and 16.70% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 97.70 males. For every 100 females age 18 and over, there were 97.70 males.
The median income for a household in the county was $36,405, and the median income for a family was $42,400. Males had a median income of $31,239 versus $21,100 for females. The per capita income for the county was $17,456. About 6.10% of families and 9.50% of the population were below the poverty line, including 12.80% of those under age 18 and 9.80% of those age 65 or over.