William Freeman Vilas (July 9, 1840–August 27, 1908) was a member of the Democratic Party who served in the United States Senate for the state of Wisconsin from 1891 to 1897.

Vilas was born in Chelsea, Vermont and moved to Madison, Wisconsin with his family in 1851. He graduated from the University of Wisconsin in Madison in 1858, and from the University at Albany Law School in 1860. He enlisted in the Union Army during the Civil War and a Captain in the Wisconsin Volunteer Infantry, and later a lieutenant colonel.

He was a Professor of Law at the University of Wisconsin, and a regent of the University from 1880 to 1885 and 1898 to 1905. Vilas served as a member of the Wisconsin State Assembly in 1885, until he was appointed the Postmaster General between 1885 and 1888, and as Secretary of the Interior from 1888 to 1889, both under President Grover Cleveland.

Vilas is interned at the Forest Hill Cemetery in Madison, Wisconsin.

|- style="text-align: center;" | width="30%" |Preceded by:
Lucius Q.C. Lamar | width="40%" style="text-align: center;" |United States Secretary of the Interior
1888–1889 | width="30%" |Succeeded by:
John W. Noble

|- style="text-align: center;" | width="30%" |Preceded by:
John Coit Spooner | width="40%" style="text-align: center;" |Class 3 U.S. Senator from Wisconsin
1891–1897 | width="30%" |Succeeded by:
John Coit Spooner