Putnam County is the least extensive county in the U.S. state of Illinois. According to the 2020 census, it had a population of 5,637.^[1] The county seat is Hennepin.^[2] The county was formed in 1825 out of Fulton County and named after Israel Putnam,^[3] who was a general in the American Revolution. Putnam County is part of the Ottawa, IL Micropolitan Statistical Area.

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Putnam County
County
Putnam County Courthouse, Hennepin
Location within the U.S. state of Illinois
Illinois's location within the U.S.
Coordinates: 41°12′N 89°17′W
Country	United States
State	Illinois
Founded	1825
Named for	Israel Putnam
Seat	Hennepin
Largest village	Granville
Area
• Total	172 sq mi (450 km2)
• Land	160 sq mi (400 km2)
• Water	12 sq mi (30 km2)  7.0%
Population  (2020)
• Total	5,637
• Density	33/sq mi (13/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional districts	14th, 16th
Website	www.co.putnam.il.us

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According to the U.S. Census Bureau, the county has a total area of 172 square miles (450 km²), of which 160 square miles (410 km²) is land and 12 square miles (31 km²) (7.0%) is water.^[4] It is the smallest county in Illinois by area.

As of the 2010 census, there were 6,006 people, 2,509 households, and 1,734 families residing in the county.^[12] The population density was 37.5 inhabitants per square mile (14.5/km²). There were 3,074 housing units at an average density of 19.2 per square mile (7.4/km²).^[4] The racial makeup of the county was 96.6% white, 0.5% black or African American, 0.2% Asian, 0.1% American Indian, 1.4% from other races, and 1.1% from two or more races. Those of Hispanic or Latino origin made up 4.2% of the population.^[12] In terms of ancestry, 46.5% were German, 16.7% were Irish, 16.3% were Italian, 10.9% were Polish, 10.1% were English, 5.1% were Swedish, and 3.5% were American.^[13]

Of the 2,509 households, 27.7% had children under the age of 18 living with them, 57.6% were married couples living together, 7.2% had a female householder with no husband present, 30.9% were non-families, and 26.0% of all households were made up of individuals. The average household size was 2.39 and the average family size was 2.85. The median age was 45.2 years.^[12]

The median income for a household in the county was $56,458 and the median income for a family was $68,875. Males had a median income of $50,205 versus $31,886 for females. The per capita income for the county was $27,004. About 6.2% of families and 10.9% of the population were below the poverty line, including 21.8% of those under age 18 and 5.4% of those age 65 or over.^[14]

This section needs additional citations for verification. (June 2021)

Prior to 1988, Putnam County was a Republican Party stronghold in presidential elections, backing the Republican candidate in all but three elections from 1892 to 1984. From 1988 to 2012, the county consistently backed Democratic Party presidential candidates, but none fared better than Illinois resident Barack Obama's 56.9% in 2008. However, he failed to win a majority of the county's votes four years later despite winning it overall in his 2012 reelection bid. This foreshadowed what was to come in the 2016 election, as the county swung 21.8 points Republican to back Donald Trump over Illinois-born Hillary Clinton by a margin of 19.9%.^[15]

• National Register of Historic Places listings in Putnam County
• Putnam County, New York