<P> The Mayo Clinic is a nonprofit medical practice and medical research group based in Rochester, Minnesota . It employs more than 4,500 physicians and scientists and 57,100 allied health staff . The practice specializes in treating difficult cases through tertiary care . It spends over $660 million a year on research . </P> <P> William Worrall Mayo settled his family in Rochester in 1863 and opened a medical practice that evolved under his sons into Mayo Clinic . Mayo Clinic is widely regarded as one of the United States' greatest hospitals and ranked No. 1 in the country on the 2016--2017 U.S. News & World Report List of "Best Hospitals" of the United States, maintaining a position near the top for more than 25 years . It has been on the list of "100 Best Companies to Work For" published by Fortune magazine for fourteen consecutive years . It continued to achieve this ranking through 2017 . </P> <P> In addition to their flagship hospital in Rochester, the Mayo Clinic has major campuses in Arizona and Florida . The Mayo Clinic Health System also operates affiliated facilities throughout Minnesota, Wisconsin, and Iowa . </P> <P> In 1863, William Worrall Mayo (1819--1911) came to Rochester, Minnesota as part of his appointment as an examining surgeon for the military draft board during the American Civil War . The city was to his liking, and his wife and children joined him in early 1864 . William Worrall Mayo opened his medical practice after the war, and served in several leadership roles in the community . Both of W.W. Mayo's sons, William James Mayo (1861--1939) and Charles Horace Mayo (1865--1939) grew up in Rochester, and when old enough both attended medical school . William graduated in 1883 and joined his father's practice, with Charles joining after he completed his training in 1888 . </P>

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