Hoover was one of three sons born to brick manufacturer William Henry Hoover and the former Lucia Leonard Peoples. The elder William, who made the brick used to construct O'Brien's Opera House, had established a plant near Russellville and hoped to establish a town for his workers there. The Panic of 1893, however, dashed his plans, and the family moved to Jasper, then spent two years in Indian territory, where young William attended a mission schoolhouse. They returned to Jasper, then moved to Bessemer in 1911.
William married the former Bertha Christian in 1910. He began taking a correspondence course in pharmacy from LaSalle University in Chicago, Illinois and worked at Gunn's Pharmacy in Bessemer. Once he earned his license, he remained there, but realized that his poor hearing made it impossible to take prescriptions over the telephone. He changed careers and became an agent for the Continental Casualty insurance company. He founded a new company, Employers Mutual, in 1921. The firm was incorporated at a meeting at the Tutwiler Hotel on October 23, 1922 and Hoover was elected vice president and general manager. It began operating on December 2 of that year. Hoover also lobbied the Alabama State Legislature to pass workmen's compensation laws. Employers Mutual went public in 1929 with Hoover as president. It continued to prosper during the Great Depression and expanded into life insurance in 1944.
Hoover was active in civic life in Birmingham and was a member of the Birmingham Chamber of Commerce and Committee of 100. He was active in the Exchange Club of Birmingham and the Birmingham Jaycees, and served as president of the Jefferson County Safety Council, where he coined the slogan "Drive carefully. The life you save may be your own," which was used nationally. He was also a director of the Southern Research Institute and president of The Club.
He was also a leading opponent of racial integration. He joined with other area businessmen to found the American States' Rights Association in 1954. The group sponsored the publication of Neo-Nazi literature and radio broadcasts by Asa Carter that attacked local voices of moderation. As the association's president, Hoover openly speculated on the need to forcibly remove African Americans from North America. He founded the Hoover Academy in West End in 1963 as a segregated alternative to Graymont Elementary School, but enrollment suffered as white families moved out of the city instead.
On November 19, 1932 Hoover married his second wife, the former Helen Gould Carnes. They bought a house at 3521 Whitehall Road in Homewood's Mayfair neighborhood. Hoover also bought 1,500 acres in Shelby County in 1936 for a $1,500 investment. In 1944 he bought 160 acres along Tyler Road on Shades Mountain and built a small log cabin there with lumber cut at Sellers Sawmill nearby. He used the cabin to host company picnics and also raised corn and feed in the section later subdivided as Mill Run.
In 1946 the family moved from Homewood to a house on Overhill Road in Mountain Brook. In 1948 Hoover swapped houses with Elliott Carper and moved the family to Surrey Road while construction of their planned new home on Tyler Road progressed. It was completed in February 1950 and the Hoovers joined the rural community of Bluff Park just as its first fire station was being built.
Hoover began buying property on Montgomery Highway in the early 1950s, eventually amassing over 680 acres. He began planning a town with residential lots along the newly laid-out Whispering Pine Circle, Helen Circle, Deo Dara Drive, Greenvale Road and Valgreen Lane. He donated 10 acres to the Jefferson County Board of Education, where Green Valley Elementary School was later built. He also donated land for the first Hoover City Hall, Hoover Fire Station No. 1 and for Star Lake Park. Hoover sold lots at a discount to encourage homebuyers. He moved the offices of Employers Insurance to the area in 1958 and developed the Green Valley Country Club in 1962. He took up the game of golf at age 72.
- "Anti-Negro Groups Mushrooming in Dixie" (December 4, 1954) Associated Negro Press/Indianapolis Recorder, p. 16 - via Hoosier State Chronicles
- Parrish, Jane Hoover (n.d.) "The History of the Family of William Henry Hoover, Sr, Founder of the City of Hoover, Alabama" Hooveral.org - accessed May 18, 2015
- Thornton, J. Mills (2002) "Dividing Lines: Municipal Politics and the Struggle for Civil Rights in Montgomery, Birmingham, and Selma" Tuscaloosa: University of Alabama Press. ISBN 9780817311704
- Bagley, Joseph Mark (2014) "School Desegregation, Law and Order, and Litigating Social Justice in Alabama, 1954-1973" PhD dissertation for Georgia State University, Department of History
- Skaggs, Heather Jones (2014) Hoover. Images of America Series. Mount Pleasant, South Carolina: Arcadia Publishing. ISBN 9781467112185