[2] In 1960, the United States Census Bureau placed the mean center of U.S. population in Clinton County.

[3] Clinton County is part of the St. Louis, MO-IL Metropolitan Statistical Area.

In 1805, prior to the establishment of the county, the territorial government established a post road from its capital (Vincennes, Indiana) to St. Louis, Missouri, passing through the county.

It extended from the Goshen Settlement to the Ohio salt works and crossed the Kaskaskia River at Carlyle.

[5] Clinton County became the home to early settlers by 1814, when the first land entries were made.

It was named for the seventh Governor of New York, DeWitt Clinton, who helped build the Erie Canal.

[12] As of the 2010 United States census, there were 37,762 people, 14,005 households, and 9,760 families residing in the county.