Born in 1840 in Vermont; his parents moved to Madison, Wisconsin when he was a small child. Vilas was admitted to the Wisconsin bar upon graduation, the outbreak of the Civil War led him to volunteer in the Union Army; he eventually rose to the rank of lieutenant colonel. At the end of the war, he returned to Wisconsin to practice law, and in 1868, he became a professor of law at the University of Wisconsin.
President Cleveland nominated Vilas to become secretary of the Interior and also served as the first Postmaster General. In 1891, the Wisconsin legislature elected Vilas to the U.S. Senate, where he served until 1897. Vilas then became a regent of the University of Wisconsin in 1898. Vilas also served as one of the members of the Madison Park and Pleasure Drive Association.
In 1904, the City of Madison received 50 acres of land from William and Anna Vilas under the conditions that it be used “for the uses and purposes of a public park and pleasure ground”. The park was named in honor of the Vilas’s son, Henry, who died at a young age from complications related to diabetes. The family stipulated that the park always be admission free.
In 1911, 28 acres of the park were partitioned into an animal exhibit, now known as the Vilas Zoo.
William died in 1908.