William Mills Fitzgerald was born November 3, 1911, in Beloit, the son of William J. and Margaret Mills Fitzgerald. The Fitzgerald family were early settlers in Beloit, having come here in 1848. His mother was a sister of Tommy Mills, well-known college coach and drama teacher.

William received his education in Beloit at Strong Elementary School and Roosevelt Junior High School. He graduated from Beloit High School, class of 1930. He was class president in his senior year and was on the varsity football and basketball teams.

He graduated from Beloit College in 1934 with a Bachelor of Science degree in geology. William was a member of Sigma Chi Fraternity and served one year as its president. He was captain and quarterback of the football team in his senior year.

William attended medical school in 1936 and 1937 at the University of Wisconsin and then went on to Northwestern University in 1939. He served his internship at City Hospital in St. Louis. He majored in internal medicine and completed his residency at City Hospital in St. Louis in 1941–42.

In 1943, William enlisted in the U.S. Naval Reserve and was assigned to the 3rd Marine Division. He served in the South Pacific as Battalion Surgeon. He saw action in Guadalcanal, Guam, and the invasion of Iwo Jima. He was discharged in 1946 as Captain in the Medical Corps.

In 1943, William married Alexandria Hoevel of St. Louis at the Naval Air Station at Corpus Christi, Texas. To this marriage, four daughters were born.

He founded Beloit Clinic in July 1947 with Dr. Kenneth Carter and Dr. Richard Sanderson, both colleagues from City Hospital in St. Louis.

William was a member of St. Thomas Catholic Church, the Beloit Elks Club, the Rock County Medical Society, the Wisconsin State Medical Society, and was past president of both the Beloit Hospital Medical Staff and Beloit Clinic Staff. He was also a member of the Beloit Booster Club.

Dr. Fitzgerald retired from active practice in 1984 and passed away on July 18, 1988.