Illinois

St. Clair

257,400
2020 population
1800
first census record
23
census records

About St. Clair

St. Clair, Illinois, first appears in the United States federal census in 1800, when it recorded a population of 1,355. At the most recent census, in 2020, its population stood at 257,400.

Its recorded population peaked at 285,176 in 1970, and has since declined by roughly 10 percent.

On the ground today, 19 documented military engagements have been recorded within the county, among them Cahokia Mound 72 Mass Sacrifice, Mississippian East St. Louis Site Violence, Cahokia Warrior Burial Mound 72, and 29 places are listed on the National Register of Historic Places.

Population by decade

Census YearPopulationChart
2020257,400
2010270,056
2000256,082
1990262,852
1980267,531
1970285,176
1960262,509
1950205,995
1940166,899
1930157,775
1920136,520
1910119,870
190086,685
189066,571
188061,806
187051,068
186037,694
185020,180
184013,631
18307,078
18205,253
18105,007
18001,355
Source

Population data from the United States decennial census, U.S. Census Bureau (public domain).

Battles & engagements in St. Clair

Military engagements that took place in St. Clair, Illinois.

Cahokia Mound 72 Mass Sacrifice
1000
Mississippian East St. Louis Site Violence
1050
Cahokia Warrior Burial Mound 72
1050
Cahokia Mound 72 Sacrificial Pit
1050
Cahokia East St. Louis Mass Sacrifice
1050
Cahokia Woodhenge Sacrificial Deposits
1050
Cahokia Mound 72 Mass Burial (Sacrifices)
1050
Lohmann Phase Cahokia Warfare
1050
Cahokia Palisade Defense Conflict
1050
Cahokia Palisade Conflict – East St. Louis
1100
Cahokia Hinterland Conflict – East St. Louis Mound Group
1100
Cahokia Warfare Period
1100
East St. Louis Mound Complex Conflict
1150
Cahokia Decline Warfare
1300
Pontiac assassinated at Cahokia 1769
1769
Capture of Cahokia (Illinois 1778)
1778
Battle of Cahokia Jul 1778
1778
Capture of Cahokia (Clark)
1778
East St. Louis Race Riot 1917
1917

Historic places in St. Clair

National Register of Historic Places listings in St. Clair, Illinois.

Martin, Pierre, House
North Dupo
Old Cahokia Courthouse
Cahokia
Emerald Mound and Village Site
Lebanon
Berger-Kiel House
Mascoutah
Hotel Belleville
Belleville
United States Post Office and Courthouse
East Saint Louis
Knobeloch-Seibert Farm
Belleville
Mermaid House Hotel
Lebanon
Downtown East St. Louis Historic District
East St. Louis
Jarrot, Nicholas, Mansion
Cahokia
Rutter Store
St. Libory
Belleville Historic District
Belleville
Lebanon Historic District
Lebanon
Spivey Building
East St. Louis
Cahokia Mounds
Collinsville
Pennsylvania Avenue Historic District
East St. Louis
Draser, George, Jr., House
Mascoutah
Tiedemann House
O'Fallon
Turkey Hill Grange Hall
Belleville
Blair Historic District
Belleville
Majestic Theatre
East St. Louis
Scott Field Historic District
O'Fallon
Marissa Academy
Marissa
Union Trust Bank Company Building
East St. Louis
Browse all Illinoishistoric sites ›

Other counties in Illinois

Explore census history and historic records for more Illinois counties.

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Everything a full report reveals about St. Clair County, Illinois

This page charts the census history of St. Clair County, Illinois. A full Aubrey report for an address here pulls together everything the historical record holds about the ground, from the earliest settlement to the twentieth century:

Overview
An interactive map of the location with historic sites, battles and Native heritage plotted, and its full story era by era.
The Land
The historic sites and place names around the location, and how this land was settled and used.
Geology
The bedrock beneath the site, its age and rock type, reaching back millions of years.
LiDAR Terrain
Laser-scanned terrain that reveals earthworks and old features hidden in the landscape.
Conflict & War
The battles, raids and skirmishes fought near here, across every era of American conflict.
The Civil War
The Civil War on this ground, 1861 to 1865: who held it, and the battles, camps and regiments nearby.
The Soldiers
The men who marched from here in the Civil War, named and traced where the record allows.
Native Heritage
The Native nations who held this land, mapped across time from before European contact to today.
Settlement
Who claimed and held this ground, from Indigenous homelands through the colonial powers to the United States.
The Community
How the town grew, who came, and what kind of place it became, traced through the census record.
Rivers & Rail
The rivers, canals and railroads that connected this place between 1830 and 1911.
Notable People
The people born, buried or genuinely tied to this exact place, with their stories.
Historical Maps
Historic maps of the location layered over how it looks today.
Finds & Access
Museum objects tied to the area, and the laws on searching, collecting and access here.
Literature
The old books, county histories and archives that mention this place, quoted with their sources.
Spotlight
A deep dive into the most remarkable, lesser-known history of the place, traced back to the record.
Points of Interest
The most significant historic sites and landmarks near the location, and why they matter.
Timeline
The whole story of the location told era by era, from first peoples to the present day.
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Illinoishistory ›NRHP historic sites ›Notable people from Illinois›

Frequently asked about St. Clair

When does St. Clair first appear in the US census?
St. Clair, Illinois first appears in the federal census in 1800, with a recorded population of 1,355.
What is the population of St. Clair?
At the most recent federal census (2020), St. Clair had a recorded population of 257,400.
When did St. Clair's population peak?
St. Clair's recorded population peaked at 285,176 in 1970.
Were any battles fought in St. Clair?
19 documented military engagements took place in St. Clair, including Cahokia Mound 72 Mass Sacrifice, Mississippian East St. Louis Site Violence, Cahokia Warrior Burial Mound 72.
How many historic places are in St. Clair?
29 sites are listed on the National Register of Historic Places in St. Clair, Illinois.
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