According to theUS Census Bureau, the county has a total area of 395 square miles (1,020 km2), of which 379 square miles (980 km2) is land and 16 square miles (41 km2) (4.1%) is water.[5]
In recent years, average temperatures in the county seat of Oquawka have ranged from a low of 15 °F (−9 °C) in January to a high of 85 °F (29 °C) in July, although a record low of −26 °F (−32 °C) was recorded in February 1996 and a record high of 105 °F (41 °C) was recorded in August 1983. Average monthly precipitation ranged from 1.31 inches (33 mm) in January to 4.48 inches (114 mm) in July.[6]
US Decennial Census[8] 1790-1960[9] 1900-1990[10] 1990-2000[11] 2010[12]
As of the2010 United States census, there were 7,331 people, 3,149 households, and 2,127 families residing in the county.[13] The population density was 19.3 inhabitants per square mile (7.5/km2). There were 3,827 housing units at an average density of 10.1 per square mile (3.9/km2).[5] 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% wereGerman, 14.5% wereIrish, 11.9% wereEnglish, 5.9% wereSwedish, and 5.0% wereAmerican.[14]
Henderson County, Illinois – Racial and ethnic composition Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.
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 thepoverty line, including 13.3% of those under age 18 and 8.3% of those age 65 or over.[24]
As part ofYankee-settledNorthern Illinois, Henderson County was solidlyWhig in its first three elections and then equally Republican from that party's formation until theGreat Depression.Franklin D. Roosevelt in 1932 was the first Democrat to win it, but the county returned to RepublicanAlf Landon in 1936 and was not won by a Democrat until the GOP nominated the southern-oriented conservativeBarry Goldwater in 1964.
After that, like many Yankee counties, it returned to its Republican roots between 1968 and 1984, but turned reliably Democratic in presidential elections from 1988 to 2012. RepublicanDonald Trump carried the county with over 61 percent of the vote in 2016; the highest percentage won by any Republican candidate sinceDwight D. Eisenhower in 1956, and for then Democratic opponent Hillary Clinton, it was the lowest by a Democrat sinceAl Smith in 1928. Republican margins have continued to improve in each subsequent election as rural Illinois shifts sharply to the right and native sonBarack Obama is no longer on the ballot, with Trump's 68% in 2024 marking the best Republican result since 1928. The county's new Republican dominance has extended to the local level as well, with Republicans going entirely unchallenged for county office.[25]