Henry County is a county located in the U.S. state of Illinois. The 2020 United States Census, listed its population at 49,284. Its county seat is Cambridge. Henry County is included in the Davenport-Moline-Rock Island, IA-IL Metropolitan Statistical Area.

Henry County was formed on January 13, 1825, out of Fulton County, Illinois. It is named for Patrick Henry, Revolutionary War firebrand and champion of individual rights, to whom the slogan "give me liberty, or give me death" is attributed. The county was settled by people from New England and western New York, descendants of English Puritans who settled New England in the colonial era. The New England settlers founded the five towns of Andover, Wethersfield, Geneseo, Morristown and La Grange.

The settlement of Cambridge came about in 1843, when the owner of the land in that area (Rev. Ithamar Pillsbury) dedicated a section of his properties to a town council; lots were sold to incoming settlers, and construction of the town proper began on June 9, 1843. The incoming "Yankee" settlers made Henry County culturally similar to early New England culture.

• 
  Henry County from the time of its creation to 1827
• 
  The county between 1827 and 1831
• 
  Henry between 1831 and 1836
• 
  Henry in 1836, after Whiteside County was created

According to the US Census Bureau, the county has a total area of 826 square miles (2,140 km), of which 823 square miles (2,130 km) is land and 2.7 square miles (7.0 km) (0.3%) is water. It is the 29th largest of Illinois' 102 counties. The area is fairly flat, with elevations ranging from 650 feet above sea level in the northwest to 850 in the southeast. About 456,596 acres (1,847.78 km) or 86.7% of the county's land area, is used for agriculture.

Cambridge, Illinois
Climate chart (explanation)
J F M A M J J A S O N D     1.5     29 13     1.6     35 19     2.7     47 30     3.7     61 40     4.2     73 52     4.2     82 61     3.9     86 66     4.3     83 63     3.3     76 55     3     63 43     2.8     47 31     2.2     33 19 █ Average max. and min. temperatures in °F █ Precipitation totals in inches Source: The Weather Channel
Metric conversion J F M A M J J A S O N D     39     −2 −11     40     2 −7     68     8 −1     95     16 4     107     23 11     107     28 16     99     30 19     110     28 17     84     24 13     76     17 6     72     8 −1     55     1 −7 █ Average max. and min. temperatures in °C █ Precipitation totals in mm

In recent years, average temperatures in the county seat of Cambridge have ranged from a low of 13 °F (−11 °C) in January to a high of 86 °F (30 °C) in July, although a record low of −24 °F (−31 °C) was recorded in February 1996 and a record high of 103 °F (39 °C) was recorded in July 1983. Average monthly precipitation ranged from 1.52 inches (39 mm) in January to 4.32 inches (110 mm) in August.

Historical population

Census	Pop.	Note	%±
1830	41		—
1840	1,260		2,973.2%
1850	3,807		202.1%
1860	20,660		442.7%
1870	35,506		71.9%
1880	36,597		3.1%
1890	33,338		−8.9%
1900	40,049		20.1%
1910	41,736		4.2%
1920	45,162		8.2%
1930	43,851		−2.9%
1940	43,798		−0.1%
1950	46,492		6.2%
1960	49,317		6.1%
1970	53,217		7.9%
1980	57,968		8.9%
1990	51,159		−11.7%
2000	51,020		−0.3%
2010	50,486		−1.0%
2020	49,284		−2.4%
2023 (est.)	48,448		−1.7%
US Decennial Census 1790-1960 1900-1990 1990-2000 2010

As of the 2010 United States Census, there were 50,486 people, 20,373 households, and 14,149 families residing in the county. The population density was 61.3 inhabitants per square mile (23.7/km). There were 22,161 housing units at an average density of 26.9 per square mile (10.4/km). The racial makeup of the county was 94.8% white, 1.6% black or African American, 0.4% Asian, 0.2% American Indian, 1.6% from other races, and 1.4% from two or more races. Those of Hispanic or Latino origin made up 4.8% of the population. In terms of ancestry, 30.0% were German, 14.6% were Irish, 12.3% were Swedish, 11.5% were English, and 7.2% were American.

Of the 20,373 households, 31.1% had children under the age of 18 living with them, 55.9% were married couples living together, 9.5% had a female householder with no husband present, 30.6% were non-families, and 26.1% of all households were made up of individuals. The average household size was 2.44 and the average family size was 2.92. The median age was 41.8 years.

The median income for a household in the county was $49,164 and the median income for a family was $61,467. Males had a median income of $44,589 versus $30,992 for females. The per capita income for the county was $24,915. About 6.8% of families and 10.4% of the population were below the poverty line, including 16.9% of those under age 18 and 8.7% of those age 65 or over.

• Annawan
• Atkinson

• Kedron
• Oxford
• Saxon

This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2021) (Learn how and when to remove this message)

Henry County's political history is fairly typical of many Yankee-settled rural counties in Illinois. After being largely Democratic in its first few elections, the county turned powerfully Republican for the 110 years following the formation of that party. The only time it did not vote Republican between 1856 and 1960 was in 1912 when the GOP was mortally divided and Progressive Theodore Roosevelt won a majority of the county's ballots. In 1964, when the Republican Party nominated the Southern-oriented Barry Goldwater, Henry County voted Democratic for the first time since 1852, but as was typical for Yankee counties it returned to the Republicans with the selection of the more moderate Richard Nixon.

In the 1980s, the transition of the Republican Party into a party largely based around Southern Evangelicals severely alienated its historic Yankee base: Henry County turned to Democrat Michael Dukakis in 1988, and voted Democratic in every election between 1988 and 2012 except that of 2004 when George W. Bush carried the county by 5.1 percent. However, concern with unemployment and trade deals in the “Rust Belt” resulted in a powerful swing to Republican Donald Trump in 2016 – the worst Democratic result in the county since Jimmy Carter in 1980. In 2020, Trump built on his win in 2016, capturing 60% of the vote - the highest Republican percentage in 40 years.

United States presidential election results for Henry County, Illinois

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	15,359	60.99%	9,226	36.64%	596	2.37%
2020	15,300	59.53%	9,797	38.12%	604	2.35%
2016	13,985	56.75%	8,871	36.00%	1,787	7.25%
2012	11,583	47.46%	12,332	50.53%	490	2.01%
2008	11,263	45.33%	13,181	53.04%	405	1.63%
2004	13,212	52.34%	11,877	47.05%	152	0.60%
2000	10,896	46.43%	11,921	50.79%	653	2.78%
1996	8,393	38.33%	11,201	51.15%	2,303	10.52%
1992	8,989	36.88%	11,077	45.45%	4,305	17.66%
1988	11,358	49.28%	11,594	50.30%	96	0.42%
1984	14,504	57.41%	10,679	42.27%	79	0.31%
1980	14,506	59.93%	7,977	32.95%	1,723	7.12%
1976	12,849	56.03%	9,822	42.83%	263	1.15%
1972	14,796	63.82%	8,368	36.09%	21	0.09%
1968	12,524	55.10%	8,455	37.20%	1,752	7.71%
1964	10,644	46.83%	12,085	53.17%	0	0.00%
1960	14,297	57.91%	10,372	42.01%	21	0.09%
1956	15,896	65.46%	8,349	34.38%	39	0.16%
1952	16,301	65.49%	8,558	34.38%	33	0.13%
1948	12,363	58.84%	8,489	40.40%	159	0.76%
1944	13,539	59.48%	9,130	40.11%	92	0.40%
1940	14,971	58.37%	10,481	40.86%	196	0.76%
1936	11,953	49.61%	11,490	47.69%	651	2.70%
1932	11,376	51.25%	10,122	45.60%	701	3.16%
1928	14,666	70.83%	5,858	28.29%	183	0.88%
1924	13,159	72.39%	1,944	10.69%	3,076	16.92%
1920	12,379	78.96%	2,530	16.14%	768	4.90%
1916	11,406	65.42%	5,220	29.94%	808	4.63%
1912	1,859	20.29%	2,219	24.22%	5,085	55.49%
1908	6,387	64.53%	2,499	25.25%	1,011	10.22%
1904	7,331	74.52%	1,390	14.13%	1,117	11.35%
1900	6,892	68.54%	2,809	27.94%	354	3.52%
1896	6,177	66.03%	2,971	31.76%	207	2.21%
1892	4,265	55.82%	2,670	34.95%	705	9.23%

• National Register of Historic Places listings in Henry County, Illinois

• Official website
• U.S. Geological Survey Geographic Names Information System: Henry County, Illinois
• Henry County Tourism Bureau
• Illinois Ancestors Henry County
• Henry County Historical Society

41°21′11″N 90°07′53″W / 41.35306°N 90.13139°W / 41.35306; -90.13139