Illinois Counties
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Illinois Counties

There are one hundred and two counties in Illinois. St. Clair County was the first county established in what is today Illinois. Most counties in Illinois were named after early American leaders, especially of the American Revolutionary War, as well as soldiers from the Battle of Tippecanoe and the War of 1812.

St. Clair County, Illinois

St. Clair County Education, Geography, and HistorySt. Clair County, Illinois Courthouse

St. Clair County is the oldest county in the state of Illinois. According to the 2010 census, it had a population of 270,056, making it the eighth most populous county in Illinois. St Clair County was created on April 27, 1790. The county seat is Belleville. The county is named for Arthur St. Clair (1737-1818), major general in the American Revolutionary War and first Governor of the Northwest Territory.

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

Etymology - Origin of St. Clair County Name

The county is named for General Arthur St. Clair, Commander in Chief of the United States Army after the American Revolution and Governor of United States Territory northwest of the Ohio River.


County QuickFacts: CensusBureau Quick Facts

St. Clair County History

St Clair County was created on April 27, 1790 (Territorial Records of the Northwest Territory, St. Clair Papers, Vol. 2, p. 165) and was formed from the Northwest Territory. Present area, or parts of it, formerly included in: St. Clair County was the first county established in Illinois, at the time a part of the Northwest Territory.

The County was named for Arthur St. Clair, a soldier of the French and Indian wars, a Major General during the Revolution, Commander-in-Chief of the Army after the Revolution, and Governor of the Territory of the United States northwest of the Ohio River. The County Seat is Belleville . Prior County Seats was Cahokia* (1790-1814), Kaskaskia* (1790-1795), Prairie du Rocher* (1790-1795) and Belleville (1814-Present).

Geography: Land and Water

As reported by the Census Bureau, the county has a total area of 674 square miles (1,746 km2), of which, 664 square miles (1,719 km2) of it is land and 10 square miles (26 km2) of it (1.51%) is water.

Saint Clair county is located in south Illinois. The central portion of St. Clair county, sitting atop the Mississippi River bluff. The eastern and southern portion of the county is scattered with older small communities between large swathes of corn and soybean fields. Frank Holten State Recreation Area and part of Kaskaskia River State Fish & Wildlife Area are located in this county.

Neighboring Counties

Bordering counties are as follows:

  • North: Madison County
  • Northeast: Clinton County
  • Southeast: Washington County
  • South: Randolph County
  • Southwest: Monroe County
  • Northwest: St. Louis County, Mo.; St. Louis city, Mo.


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