Was the movie outlaw Josey Wales based on a real person?

No. Josey Wales is a fictional character. He was created by Forrest Carter, for the novel Gone to Texas.

Josey Wales is a Fictional_charactercreated by author Forrest_Carter, for his NovelGone_to_Texas.

You're wrong. He was based on the Bushwhacker Bill Wilson. Check it out. He is even called "Mr. Wilson" near the end.