COUNTY ORGANIZED: 1812.  

COUNTY NAMED FOR:  French King Louis IX, known as Saint Louis.

COUNTY SEATS: The City of St. Louis was the original county seat.  However, the City seceded from St. Louis County in March 1877, allowing it to become an independent city and limiting its political boundaries.  Clayton is an inner-ring suburb of St. Louis.

COUNTY SEAT NAMED FOR: Ralph Clayton, who donated the land for the courthouse.

STANDING: 

• 1864 Courthouse that is now part of the Jefferson National Expansion Memorial that includes the Gateway Arch.   The corner stone was laid in 1839 but redesign efforts in 1851 and 1861 delayed completion until 1864.  In 1877 the city of St. Louis split from the county and the building became city property at that time.   
• 1945 Courthouse in Clayton that now serves as the County Police headquarters.
• 1971 County Government plaza and modern six-story courthouse in Clayton.