In the Senate Elections Data Project 1871-1913, largely funded by a National Science Foundation grant (NSF 0517813; Principal Investigator, Wendy J. Schiller) we have collected the roll call votes from state and house state journals for all identified elections for U.S. senator held in during this time period. We have also collected data on the state legislators who cast these votes, and identified the universe of candidates who sought and won Senate seats during this time period. Where we could, we also collected data on chamber officer votes, and election returns for state legislatures, as well as a large collection of primary source newspaper articles about these elections. There has never been a systematic account of how indirect elections worked across all states, especially with respect to how candidates were nominated and elected, the nature of the conflict over these seats, and the role and strength of party organizations in influencing the outcome. It is our hope that making this data public will encourage others to ask and answer other important questions about electoral systems, legislative behavior, American history, and the efficacy of changing the Constitution to produce more responsive government.