William James Mayo, American physician and surgeon, co-founded the Mayo Clinic (died 1939)

William James Mayo was a physician and surgeon in the United States and one of the seven founders of the Mayo Clinic. He and his brother, Charles Horace Mayo, both joined their father's private medical practice in Rochester, Minnesota, after graduating from medical school in the 1880s. In 1919, that practice became the not-for-profit Mayo Clinic.

Mayo Clinic is a private American academic medical center focused on integrated healthcare, education, and research. It maintains three major campuses in Rochester, Minnesota; Jacksonville, Florida; and Phoenix/Scottsdale, Arizona.