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St. Clair County, Illinois facts for kids

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St. Clair County
St. Clair County Courthouse in Belleville
St. Clair County Courthouse in Belleville
Flag of St. Clair County
Flag
Map of Illinois highlighting St. Clair County
Location within the U.S. state of Illinois
Map of the United States highlighting Illinois
Illinois's location within the U.S.
Country  United States
State  Illinois
Founded 1790
Named for Arthur St. Clair
Seat Belleville
Largest city Belleville
Area
 • Total 674 sq mi (1,750 km2)
 • Land 658 sq mi (1,700 km2)
 • Water 16 sq mi (40 km2)  2.4%
Population
 (2020)
 • Total 257,400
 • Density 381.9/sq mi (147.45/km2)
Time zone UTC−6 (Central)
 • Summer (DST) UTC−5 (CDT)
Congressional district 12th
Victorian home restored
House in Lebanon, Il historic district
Mermaid House Hotel
Mermaid House Hotel, Lebanon, Illinois

St. Clair County is the oldest county in Illinois; its western border is formed by the Mississippi River, bordering Missouri. It is a part of the Metro East in southern Illinois. According to the 2020 United States Census, it had a population of 257,400, making it the eighth-most populous county in Illinois and the most populous in the southern portion of the state. Its county seat is Belleville. The county was founded in 1790 by the government of the Northwest Territory, from the western half of Knox County, before the establishment of Illinois as a state as the base for the Illinois Territory. Cahokia Village in the county was founded in 1697 and was a French settlement and former Jesuit mission.

St. Clair County is part of the American Bottom or Metro-East area of the St. Louis, MO-IL Metropolitan Statistical Area.

In 1970, the United States Census Bureau placed the mean center of U.S. population in St. Clair County.

Demographics

Historical population
Census Pop.
1820 5,253
1830 7,078 34.7%
1840 13,631 92.6%
1850 20,180 48.0%
1860 37,694 86.8%
1870 51,068 35.5%
1880 61,806 21.0%
1890 66,571 7.7%
1900 86,685 30.2%
1910 119,870 38.3%
1920 136,520 13.9%
1930 157,775 15.6%
1940 166,899 5.8%
1950 205,995 23.4%
1960 262,509 27.4%
1970 285,176 8.6%
1980 267,531 −6.2%
1990 262,852 −1.7%
2000 256,082 −2.6%
2010 270,056 5.5%
2020 257,400 −4.7%
US Decennial Census
1790-1960 1900-1990
1990-2000 2010-2019

As of the 2010 United States Census, there were 270,056 people, 105,045 households, and 70,689 families residing in the county. The population density was 410.6 inhabitants per square mile (158.5/km2). There were 116,249 housing units at an average density of 176.7 per square mile (68.2/km2). The racial makeup of the county was 64.6% white, 30.5% black or African American, 1.2% Asian, 0.2% American Indian, 0.1% Pacific islander, 1.2% from other races, and 2.2% from two or more races. Those of Hispanic or Latino origin made up 3.3% of the population. In terms of ancestry, 27.5% were German, 11.1% were Irish, 7.4% were English, and 4.6% were American.

Of the 105,045 households, 34.7% had children under the age of 18 living with them, 44.6% were married couples living together, 17.7% had a female householder with no husband present, 32.7% were non-families, and 27.5% of all households were made up of individuals. The average household size was 2.53 and the average family size was 3.09. The median age was 36.9 years.

The median income for a household in the county was $48,562 and the median income for a family was $61,042. Males had a median income of $47,958 versus $34,774 for females. The per capita income for the county was $24,770. About 12.3% of families and 15.5% of the population were below the poverty line, including 24.7% of those under age 18 and 9.7% of those age 65 or over.

Transportation

Major highways

  • I-55.svg Interstate 55
  • I-64.svg Interstate 64
  • I-70.svg Interstate 70
  • I-255.svg Interstate 255
  • US 40.svg U.S. Highway 40
  • US 50.svg U.S. Highway 50
  • Illinois 3.svg Illinois Route 3
  • Illinois 4.svg Illinois Route 4
  • Illinois 13.svg Illinois Route 13
  • Illinois 15.svg Illinois Route 15
  • Illinois 111.svg Illinois Route 111
  • Illinois 156.svg Illinois Route 156
  • Illinois 157.svg Illinois Route 157
  • Illinois 158.svg Illinois Route 158
  • Illinois 159.svg Illinois Route 159
  • Illinois 161.svg Illinois Route 161
  • Illinois 163.svg Illinois Route 163
  • Illinois 177.svg Illinois Route 177
  • Illinois 203.svg Illinois Route 203

Public transit

St. Clair County is home to 11 St. Louis MetroLink stations on the Red and Blue Lines.

  • East Riverfront
  • 5th & Missouri
  • Emerson Park
  • Jackie Joyner-Kersee Center
  • Washington Park
  • Fairview Heights
  • Memorial Hospital
  • Swansea
  • Belleville
  • College
  • Shiloh-Scott

St. Clair County is also served by Metrobus and Madison County Transit.

Adjacent counties and city

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