[2] A notable archaeological area, the Koster Site, has produced evidence of more than 7,000 years of human habitation.

Artifacts from the site are displayed at the Center for American Archeology in Kampsville, Illinois.

This left Greene county with approximately 546 square miles of land located in western-central Illinois near the Illinois River, which was an important resource that provided both a means for travel and to ship goods.

[7] As of the 2010 United States Census, there were 13,886 people, 5,570 households, and 3,777 families living in the county.

[16] The population ranking of the following table is based on the 2020 census of Greene County.

Not until considerable anti-Catholic sentiment against Al Smith turned many voters to Herbert Hoover did the county support a Republican presidential nominee.

However, with the coming of World War II, opposition to American involvement led to gains for Wendell Willkie and Thomas E. Dewey, although apart from the 1960 election – also influenced by Catholicism – Greene was a bellwether county throughout the period from 1928 to 2004.