According to the US Census Bureau, the county has a total area of, of which is land and is water.
Climate and weather
In recent years, average temperatures in the county seat of Oquawka have ranged from a low of in January to a high of in July, although a record low of was recorded in February 1996 and a record high of was recorded in August 1983. Average monthly precipitation ranged from in January to in July.
As of the 2010 United States Census, there were 7,331 people, 3,149 households, and 2,127 families residing in the county. The population density was. There were 3,827 housing units at an average density of. The racial makeup of the county was 98.2% white, 0.2% Asian, 0.2% American Indian, 0.2% black or African American, 0.1% Pacific islander, 0.2% from other races, and 1.0% from two or more races. Those of Hispanic or Latino origin made up 1.1% of the population. In terms of ancestry, 24.4% were German, 14.5% were Irish, 11.9% were English, 5.9% were Swedish, and 5.0% were American. Of the 3,149 households, 26.9% had children under the age of 18 living with them, 54.9% were married couples living together, 8.7% had a female householder with no husband present, 32.5% were non-families, and 27.3% of all households were made up of individuals. The average household size was 2.31 and the average family size was 2.78. The median age was 47.2 years. The median income for a household in the county was $43,450 and the median income for a family was $55,154. Males had a median income of $41,052 versus $27,426 for females. The per capita income for the county was $22,492. About 7.8% of families and 11.4% of the population were below the poverty line, including 13.3% of those under age 18 and 8.3% of those age 65 or over.
Politics
As part of Yankee-settled Northern Illinois, Henderson County was solidly Whig in its first three elections and then equally Republican from that party's formation until the Great Depression. Franklin D. Roosevelt in 1932 was the first Democrat to win it, but the county returned to Republican Alf Landon in 1936 and was not won by a Democrat until the GOP nominated the southern-oriented conservative Barry Goldwater in 1964. After that, like many Yankee counties, it returned to its Republican roots between 1968 and 1984, but with the shift of the GOP to a Southern Evangelical perspective Henderson County turned reliably Democratic in presidential elections from 1988 to 2012. Economic concerns in the “Rust Belt” led populist Republican Donald Trump to carry the county with over 61 percent of the vote in 2016; the highest percentage won by any Republican candidate since Dwight D. Eisenhower in 1956, and the lowest by a Democrat since Al Smith in 1928. Henderson County is located in Illinois's 17th Congressional District and is currently represented by Democrat Cheri Bustos. For the Illinois House of Representatives, the county is located in the 94th district and is currently represented by Republican Randy Frese. The county is located in the 47th district of the Illinois Senate, and is currently represented by Republican Jil Tracy.
