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. He was a prominent Bourbon Democrat.
Vilas was born in Chelsea, Vermont, the son of Esther Greene (Smilie) and Levi Baker Vilas, a politician. Vilas moved to Madison, Wisconsin with his family in 1851. He graduated from the University of Wisconsin in 1858, and from the Albany Law School in 1860. He enlisted in the Union Army during the Civil War and was a captain in the 23rd Wisconsin Volunteer Infantry Regiment and later served as the lieutenant colonel of that regiment.
Following the war, Vilas was a Professor of Law at the University of Wisconsin–Madison, 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.
He married Anna M. Fox, who had been born in the territory of Wisconsin. Their younger son died in early childhood and their elder daughter, Nellie, died in 1893. The surviving children were Henry and Mary Esther.