The 1891 United States Senate election in Wisconsin was held in the 40th Wisconsin Legislature on January 28, 1891. Incumbent Republican U.S. senator John C. Spooner ran for a second term, but lost the election to former U.S. postmaster general and U.S. secretary of the interior William F. Vilas.[1][2]
In the 1891 term, Democrats held significant majorities in both chambers of the Wisconsin Legislature, so had more than enough votes to elect a Democratic United States senator. This was the first time the Democrats were able to elect a U.S. Senator in Wisconsin since the election of Henry Dodge in 1851.