Hamilton is a city in Hancock County, Illinois, United States. The population was 2,753 at the 2020 census, a decline from 2,951 in 2010. The city is located directly across the Mississippi River from Keokuk, Iowa. Hamilton is the largest city in Hancock County.

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Hamilton was laid out in 1852 by several men in the area, including Samuel Gordon and Bryant Bartlett. Hamilton was officially incorporated as a town in 1854, and then re-incorporated as a city in 1859. Artois Hamilton, for whom the town was named, was also active in the early history of the town.

According to the 2021 census gazetteer files, Hamilton has a total area of 5.36 square miles (13.88 km), of which 3.56 square miles (9.22 km) (or 66.50%) is land and 1.79 square miles (4.64 km) (or 33.50%) is water.

Hamilton and Keokuk share Lock & Dam 19 on the Mississippi River. The dam has the largest fall of any on the Mississippi and the power house supplies a majority of the electricity for St. Louis, MO. Lake Cooper, formed above the dam, represents the widest span of the Mississippi between Montrose, IA and Nauvoo, IL.

Historical population

Census	Pop.	Note	%±
1880	1,025		—
1890	1,301		26.9%
1900	1,344		3.3%
1910	1,627		21.1%
1920	1,698		4.4%
1930	1,687		−0.6%
1940	1,642		−2.7%
1950	1,776		8.2%
1960	2,228		25.5%
1970	2,764		24.1%
1980	3,509		27.0%
1990	3,281		−6.5%
2000	3,029		−7.7%
2010	2,951		−2.6%
2020	2,753		−6.7%
U.S. Decennial Census

As of the 2020 census there were 2,753 people, 1,137 households, and 684 families residing in the city. The population density was 514.10 inhabitants per square mile (198.50/km). There were 1,308 housing units at an average density of 244.26 per square mile (94.31/km). The racial makeup of the city was 93.32% White, 0.91% African American, 0.22% Native American, 0.69% Asian, 0.00% Pacific Islander, 1.09% from other races, and 3.78% from two or more races. Hispanic or Latino of any race were 1.93% of the population.

There were 1,137 households, out of which 31.7% had children under the age of 18 living with them, 48.28% were married couples living together, 8.71% had a female householder with no husband present, and 39.84% were non-families. 31.49% of all households were made up of individuals, and 16.62% had someone living alone who was 65 years of age or older. The average household size was 3.06 and the average family size was 2.41.

The city's age distribution consisted of 23.4% under the age of 18, 7.2% from 18 to 24, 24.6% from 25 to 44, 24.3% from 45 to 64, and 20.4% who were 65 years of age or older. The median age was 40.9 years. For every 100 females, there were 80.1 males. For every 100 females age 18 and over, there were 83.7 males.

The median income for a household in the city was $49,566, and the median income for a family was $81,026. Males had a median income of $51,923 versus $29,063 for females. The per capita income for the city was $30,152. About 8.5% of families and 10.4% of the population were below the poverty line, including 21.2% of those under age 18 and 3.9% of those age 65 or over.

Hamilton Community Unit School District #328 consists of Hamilton Elementary, Hamilton Junior High School, and Hamilton High School. The school's nickname is the Cardinals, but is switching over to Titans with the sports co-op with Warsaw and Nauvoo schools. The only sports that will still be "Cardinals" are Scholastic Bowl and Junior High and Elementary sports. In 2008, the newly co-oped West Hancock (Hamilton, Warsaw, Nauvoo-Colusa) Girls basketball team took first place in the IHSA Class 2A Championship. It is the first year of the co-op basketball team, and their first championship.

• Russell Lee Arms, actor and singer who starred on Your Hit Parade television program; lived in Hamilton at the end of his life
• John Brock, MLB catcher for the St. Louis Cardinals
• Alden W. Clausen, president of the World Bank and CEO of Bank of America

• City of Hamilton official website