Whiteside County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 55,691. Its county seat is Morrison. The county is bounded on the west by the Mississippi River. Whiteside County comprises the Sterling, IL Micropolitan Statistical Area, which is also included in the Dixon-Sterling, IL Combined Statistical Area. U.S. President Ronald Reagan was born in 1911 in the Whiteside County community of Tampico.

This area was long occupied by varying cultures of Native Americans.

Whiteside County was organized by European Americans in 1836 from parts of Jo Daviess and Henry counties. It was named for General Samuel Whiteside, an Illinois officer in the War of 1812 and Black Hawk War.

Whiteside County's boundaries have remained unchanged since its creation in 1836.

According to the U.S. Census Bureau, the county has a total area of 697 square miles (1,810 km), of which 684 square miles (1,770 km) is land and 12 square miles (31 km) (1.8%) is water.

Morrison, Illinois
Climate chart (explanation)
J F M A M J J A S O N D     1.5     29 10     1.5     34 15     2.8     47 27     3.7     60 37     4.4     72 48     4.6     82 58     3.7     85 62     4.7     83 59     2.9     76 51     2.8     64 39     2.9     47 28     2.1     34 16 █ 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 −12     38     1 −9     71     8 −3     94     16 3     112     22 9     116     28 14     94     29 17     119     28 15     73     24 11     72     18 4     74     8 −2     54     1 −9 █ Average max. and min. temperatures in °C █ Precipitation totals in mm

In recent years, average temperatures in the county seat of Morrison have ranged from a low of 10 °F (−12 °C) in January to a high of 85 °F (29 °C) in July, although a record low of −30 °F (−34 °C) was recorded in February 1905 and a record high of 112 °F (44 °C) was recorded in July 1936. Average monthly precipitation ranged from 1.51 inches (38 mm) in February to 4.69 inches (119 mm) in August.

• Carroll County (north)
• Ogle County (northeast)
• Lee County (east)
• Bureau County (southeast)
• Henry County (south)
• Rock Island County (southwest)
• Clinton County, Iowa (west)

• Upper Mississippi River National Wildlife and Fish Refuge (part)

Historical population

Census	Pop.	Note	%±
1840	2,514		—
1850	5,361		113.2%
1860	18,737		249.5%
1870	27,503		46.8%
1880	30,885		12.3%
1890	30,854		−0.1%
1900	34,710		12.5%
1910	34,507		−0.6%
1920	36,174		4.8%
1930	39,019		7.9%
1940	43,338		11.1%
1950	49,336		13.8%
1960	59,887		21.4%
1970	62,877		5.0%
1980	65,970		4.9%
1990	60,186		−8.8%
2000	60,653		0.8%
2010	58,498		−3.6%
2020	55,691		−4.8%
2023 (est.)	54,498		−2.1%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010

As of the 2010 United States census, there were 58,498 people, 23,740 households, and 16,005 families residing in the county. The population density was 85.5 inhabitants per square mile (33.0/km). There were 25,770 housing units at an average density of 37.7 per square mile (14.6/km). The racial makeup of the county was 92.2% white, 1.3% black or African American, 0.5% Asian, 0.3% American Indian, 3.5% from other races, and 2.2% from two or more races. Those of Hispanic or Latino origin made up 11.0% of the population. In terms of ancestry, 32.5% were German, 15.5% were Irish, 8.7% were Dutch, 8.6% were English, and 6.0% were American.

Of the 23,740 households, 30.4% had children under the age of 18 living with them, 51.5% were married couples living together, 11.0% had a female householder with no husband present, 32.6% were non-families, and 27.7% of all households were made up of individuals. The average household size was 2.42 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 $45,266 and the median income for a family was $54,242. Males had a median income of $41,862 versus $29,157 for females. The per capita income for the county was $23,405. About 8.2% of families and 11.2% of the population were below the poverty line, including 17.6% of those under age 18 and 5.8% of those age 65 or over.

• Fulton
• Morrison (county seat)
• Prophetstown
• Rock Falls
• Sterling

• Como

Whiteside County is divided into these townships:

United States presidential election results for Whiteside County, Illinois

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	14,898	56.33%	11,012	41.64%	537	2.03%
2020	14,527	52.95%	12,253	44.67%	653	2.38%
2016	12,615	49.31%	11,035	43.14%	1,932	7.55%
2012	10,448	40.45%	14,833	57.43%	547	2.12%
2008	10,883	40.32%	15,607	57.82%	504	1.87%
2004	12,959	48.22%	13,723	51.07%	191	0.71%
2000	11,252	45.30%	12,886	51.88%	699	2.81%
1996	8,859	37.95%	11,913	51.03%	2,572	11.02%
1992	10,146	37.37%	12,329	45.41%	4,678	17.23%
1988	12,978	53.05%	11,328	46.31%	156	0.64%
1984	16,743	59.59%	11,226	39.96%	127	0.45%
1980	17,389	66.72%	7,191	27.59%	1,484	5.69%
1976	14,308	55.34%	11,255	43.53%	291	1.13%
1972	17,305	68.40%	7,909	31.26%	87	0.34%
1968	15,177	61.86%	8,132	33.15%	1,225	4.99%
1964	12,940	50.79%	12,536	49.21%	0	0.00%
1960	17,434	65.56%	9,112	34.27%	46	0.17%
1956	17,589	73.95%	6,158	25.89%	37	0.16%
1952	17,294	73.28%	6,238	26.43%	67	0.28%
1948	12,922	70.32%	5,299	28.84%	154	0.84%
1944	14,162	71.21%	5,555	27.93%	171	0.86%
1940	15,752	67.77%	7,356	31.65%	134	0.58%
1936	12,666	59.62%	7,982	37.57%	595	2.80%
1932	11,388	61.14%	7,010	37.64%	228	1.22%
1928	13,580	76.60%	4,079	23.01%	69	0.39%
1924	11,532	74.04%	1,957	12.56%	2,087	13.40%
1920	10,923	81.74%	1,927	14.42%	513	3.84%
1916	10,045	69.24%	3,839	26.46%	623	4.29%
1912	1,437	18.64%	1,996	25.89%	4,278	55.48%
1908	5,257	65.74%	2,140	26.76%	600	7.50%
1904	5,636	71.17%	1,546	19.52%	737	9.31%
1900	5,663	65.19%	2,758	31.75%	266	3.06%
1896	5,577	65.43%	2,788	32.71%	159	1.87%
1892	3,819	54.00%	2,779	39.30%	474	6.70%

Whiteside County has a political history typical of Northern Illinois. Between its first election in 1840, and 1852, it always favored the Whig Party, and although Whiteside was not as strong for the Free Soil Party as counties to the east like Boone and Lake, it gave substantial votes to that party in 1848 and 1852 and became powerfully Republican for the next century-and-a-quarter. Between 1856 and 1988 the only time Whiteside County did not vote for the Republican candidate was in 1912, when the GOP was mortally divided and Whiteside County voted for Progressive Party nominee and former President Theodore Roosevelt by a 2-to-1 margin over conservative incumbent William Howard Taft. Between at least 1880 and 1960, no Democratic presidential nominee ever won 40 percent of Whiteside County's vote, and even Alf Landon in 1936 carried the county by 22 percent when losing 46 of 48 states.

In 1964 the Republican Party nominated Barry Goldwater, whose hostility to the Yankee establishment and strongly conservative policies were sufficient to leave many traditional Republicans to stay home or even to vote for Lyndon Johnson. In this climate, Goldwater managed to keep the Republican Party's winning streak in Whiteside alive, but by just 1.6%, or 404 votes.

The county continued to vote comfortably more Republican than the nation for the next four elections. However, it began trending away from the GOP in 1984, as its most famous native, Ronald Reagan, successfully sought a second term. Even as Reagan increased his national margin by over 8%, his margin in Whiteside was more than halved, from a little over 40% in 1980 to 19.6% in 1984. The county was only marginally more Republican than the nation in 1984. The trend continued in 1988, as George H. W. Bush carried it by 6.8%, a somewhat smaller margin than he won the national popular vote by, making this election the first one in which Whiteside voted more Democratic than the nation in at least a century. In 1992, it gave Bill Clinton a plurality win, with a comfortable 8.0% margin over George H. W. Bush. In 1996, the county gave Bill Clinton an outright majority. The county went on to vote Democratic for the next four consecutive elections, giving Gore, Kerry, and Obama four straight majorities.

However, in 2016, concerns over long-term economic decline saw much of the Rust Belt swing heavily towards Donald Trump, and Whiteside flipped from a 16.9% Obama win in 2012 to a Trump plurality in 2016. In 2020, Trump won a majority—the first for a Republican since 1988—and increased his margin from 6.2% to 8.3%.

K-12 School districts include:

There is one secondary school district, Rock Falls Township High School District 301.

Elementary school districts include:

• East Coloma-Nelson Consolidated Elementary School District 20
• Montmorency Community Consolidated School District 145
• Rock Falls Elementary School District 13

• List of counties in Illinois
• National Register of Historic Places listings in Whiteside County, Illinois

• County History
• History of Whiteside
• County website

41°45′N 89°55′W / 41.75°N 89.91°W / 41.75; -89.91