Henderson County, Illinois
Henderson County Courthouse, Oquawka
Location within the U.S. state of Illinois
Illinois's location within the U.S.
|Named for||Richard Henderson|
|• Total||395 sq mi (1,020 km2)|
|• Land||379 sq mi (980 km2)|
|• Water||16 sq mi (40 km2) 4.1%|
| • Estimate |
|• Density||19/sq mi (7.2/km2)|
|Time zone||UTC−6 ( Central)|
|• Summer ( DST)||UTC−5 ( CDT)|
Henderson County was formed in 1841 from a portion of Warren County. It was named for Henderson County, Kentucky, which was named for Richard Henderson,  founder of the Transylvania Company, an early attempt to organize what later became Kentucky around 1775.
|Climate chart ( explanation)|
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. 
|US Decennial Census
1790-1960  1900-1990 
1990-2000  2010-2017 
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 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).  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. 
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.
Henderson County is divided into eleven townships:
- Big River State Forest - 2,900 acre preserve adjacent to the Mississippi River (1925)
- Delabar State Park - 89 acre preserve adjacent to the Mississippi River (1960)
- Oquawka State Wildlife Refuge 
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- "Find a County". National Association of Counties. Archived from the original on May 31, 2011. Retrieved June 7, 2011.
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- "Population, Housing Units, Area, and Density: 2010 - County". US Census Bureau. Retrieved July 11, 2015.
- "Monthly Averages for Oquawka IL". The Weather Channel. Retrieved January 27, 2011.
- "Population and Housing Unit Estimates". Retrieved November 6, 2019.
- "US Decennial Census". US Census Bureau. Archived from the original on April 26, 2015. Retrieved July 5, 2014.
- "Historical Census Browser". University of Virginia Library. Retrieved July 5, 2014.
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- "Selected Social Characteristics in the United States – 2006-2010 American Community Survey 5-Year Estimates". US Census Bureau. Retrieved July 11, 2015.
- "Selected Economic Characteristics – 2006-2010 American Community Survey 5-Year Estimates". US Census Bureau. Retrieved July 11, 2015.
- Leip, David. "Atlas of US Presidential Elections". uselectionatlas.org. Retrieved November 6, 2018.
- Henderson County IL Google Maps (accessed 19 December 2018)
- Oquawka State Wildlife Refuge Illinois State Parks (accessed 19 December 2018)
- History of Mercer and Henderson Counties, Together with Biographical Matter, Statistics, Etc. Chicago: H.H. Hill and Company, 1882.
- Henderson County Public Library District
- Henderson County Economic Development Corporation
- Henderson County Genealogy
- Henderson County Tombstone Project