* Definition of "Western": The genre isn't always clearly defined. Some films blur the lines between Westerns and other genres (action, adventure, etc.).
* Different Sources: Different sources may count different films as Westerns. Some might focus on the "classic" Western, while others might include more loosely connected films.
However, based on various sources, it's safe to say that John Wayne starred in over 50 Western films throughout his career.
To get a more specific idea, you can search for lists of John Wayne's films that are specifically categorized as Westerns.