St. Clair County is a county located in the western portion of the U.S. state of Missouri. As of the 2020 census, the population was 9,284.^[1] Its county seat is Osceola.^[2] The largest city is Appleton City. The county was organized in 1841 and named after General Arthur St. Clair, Governor of the Northwest Territory.^[3] St. Clair was also the 9th president of the United States in Congress Assembled. Under his presidency, the Northwest Ordinance and United States Constitution were passed.^[4]

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St. Clair County
County
St. Clair County courthouse in Osceola
Location within the U.S. state of Missouri
Missouri's location within the U.S.
Coordinates: 38°02′N 93°46′W
Country	United States
State	Missouri
Founded	January 29, 1841
Named for	Arthur St. Clair
Seat	Osceola
Largest city	Appleton City
Area
• Total	702 sq mi (1,820 km2)
• Land	670 sq mi (1,700 km2)
• Water	32 sq mi (80 km2)  4.6%
Population  (2020)
• Total	9,284
• Density	13/sq mi (5.1/km2)
Time zone	UTC−6 (Central)
• Summer (DST)	UTC−5 (CDT)
Congressional district	4th
Website	www.stclaircomo.com

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According to the April 1907 issue of The Century Magazine, for well over 30 years (dating from 1870) St. Clair County was in open rebellion against the U.S. Government, refusing to pay interest on bonds which it had issued to assist in the building of a railroad, which was never built.

According to the U.S. Census Bureau, the county has a total area of 702 square miles (1,820 km²), of which 670 square miles (1,700 km²) is land and 32 square miles (83 km²) (4.6%) is water.^[5]

As of the census^[11] of 2000, there were 9,652 people, 4,040 households, and 2,791 families residing in the county. The population density was 14 people per square mile (5.4 people/km²). There were 5,205 housing units at an average density of 8 units per square mile (3.1/km²). The racial makeup of the county was 97.36% White, 0.23% Black or African American, 0.75% Native American, 0.15% Asian, 0.02% Pacific Islander, 0.29% from other races, and 1.21% from two or more races. Approximately 0.98% of the population were Hispanic or Latino of any race.

There were 4,040 households, out of which 26.30% had children under the age of 18 living with them, 57.60% were married couples living together, 7.70% had a female householder with no husband present, and 30.90% were non-families. 27.40% of all households were made up of individuals, and 14.80% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.83.

In the county, the population was spread out, with 23.00% under the age of 18, 5.60% from 18 to 24, 22.90% from 25 to 44, 27.20% from 45 to 64, and 21.30% who were 65 years of age or older. The median age was 44 years. For every 100 females there were 98.60 males. For every 100 females age 18 and over, there were 94.30 males.

The median income for a household in the county was $25,321, and the median income for a family was $31,498. Males had a median income of $23,231 versus $18,351 for females. The per capita income for the county was $14,025. About 16.20% of families and 19.60% of the population were below the poverty line, including 25.30% of those under age 18 and 17.60% of those age 65 or over.

• National Register of Historic Places listings in St. Clair County, Missouri