William James Mayo, American physician and surgeon, co-founded the Mayo Clinic (d. 1939)
William James Mayo (June 29, 1861 – July 28, 1939) 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, US, after graduating from medical school in the 1880s. In 1919, that practice became the not-for-profit Mayo Clinic.

Augustus Stinchfield was also asked to join the medical practice in 1892 by William Worrall Mayo. Once Stinchfield was hired, W. W. Mayo retired at age 73. Others who were invited to be part of the enterprise were C. Graham, E. Starr Judd, Henry Stanley Plummer, Melvin Millet and Donald Balfour.