St. Clair County is named for Arthur St. Clair, who was a general and Commander in Chief of the United States Army after the American Revolution, and was Governor of the territory northwest of Ohio.
Surrounding County Courthouses:
N – Madison County
E – Clinton County and Washington County
S – Randolph County and Monroe County
W – Monroe County, St. Louis County, Missouri and St. Louis City, Missouri
Created: April 27, 1790 
County Seat:
Cahokia 1790 – 1814
Belleville 1814 – present
County Courthouse – Belleville
Location: 10 Public Square / South Illinois Street
Built: 1972 – 1976
Style: Modern
Architect: Hellmuth, Obata & Kasabaum and Weisentstein, Hausmann, Ganschinietz and Klingel, Inc.
Contractor: Bauer Brothers Construction Company
Description: The building faces north and is a six story buff concrete and glass structure. The building is located on landscaped grounds in the center of Belleville. The complex has a south building and a west building connected by a glass center section in the southwest corner. The windows of each building are horizontal on each story. The roof line is flat. In the northeast corner is a public square with two reflecting ponds with fountains.
Note: The court action to save the fifth county courthouse failed and the building was demolished in 1972. The contractor for the sixth county courthouse, Bauer Brothers Construction Company went bankrupt.
See: The 20th Judicial District includes Monroe County, Perry County, Randolph County and Washington County.
History: The county was created in 1790 and Cahkia was selected as the county seat. The first courthouse was a one story log cabin structure built by Francois Soulder in 1792. The county seat was moved to Belleville ( Compton Hill ) in 1814. The second courthouse was a long one story log structure owned my George Blair and located on the public square. The third courthouse was built in 1817. The fourth courthouse was a federal brick structure in 1827 to 1833. The fifth courthouse was designed and constructed by Robert Mitchel in 1859 to 1861. An addition was constructed in 1881 by Bailey & O Kroener. A further addition was designed by Reister & Rubach in 1910. The sixth and present courthouse was constructed in 1972 to 1976.
County Courthouse - Belleville
Commissioner Minutes 1969 – contractor
Photos taken 2007 and 2012