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.^[1] Its county seat is Morrison.^[2] 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.

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Whiteside County
County
Whiteside County Courthouse, Morrison
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Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 41°45′N 89°55′W
Country	United States
State	Illinois
Founded	1836
Named for	Samuel Whiteside
Seat	Morrison
Largest city	Sterling
Area
• Total	697 sq mi (1,810 km2)
• Land	684 sq mi (1,770 km2)
• Water	12 sq mi (30 km2)  1.8%
Population  (2020)
• Total	55,691
• Density	80/sq mi (31/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional district	17th
Website	www.whiteside.org

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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 km²), of which 684 square miles (1,770 km²) is land and 12 square miles (31 km²) (1.8%) is water.^[3]

As of the 2010 United States Census, there were 58,498 people, 23,740 households, and 16,005 families residing in the county.^[11] The population density was 85.5 inhabitants per square mile (33.0/km²). There were 25,770 housing units at an average density of 37.7 per square mile (14.6/km²).^[3] 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.^[11] 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.^[12]

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.^[11]

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.^[13]

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^[15] and 1852^[16] 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.^[17] 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,^[18] 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%.

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