You can cite Wikipedia. Here is an example:
Chicago Style (Notes and Bibliography)Format:
"Title of Article." Wikipedia. Last modified Month Day, Year. URL.Example:
"Sumner County, Tennessee." Wikipedia. Last modified July 27, 2025. https://en.wikipedia.org/wiki/Sumner_County,_Tennessee.
Notes: For Chicago Author-Date style, adapt to:
Wikipedia. 2025. "Sumner County, Tennessee." Last modified July 27, 2025. https://en.wikipedia.org/wiki/Sumner_County,_Tennessee.
But of course Wikipedia is not a source. What you need to do is read the Wikipedia article and find out where the editor found that fact and then go get a copy of that book and find that fact in the book and cite that as your source!