The 2004 United States Senate election in Iowa was held on November 2, 2004. Incumbent RepublicanUnited States SenatorChuck Grassley ran for re-election to a fifth term in the United States Senate. Grassley and former State SenatorArthur A. Small won the Republican and Democratic primaries, respectively, unopposed, and faced each other in the general election. Though this election coincided with the highly competitive presidential election, Grassley was not considered vulnerable and defeated Small in a landslide. As of 2022, this is the last time a Republican Senate candidate won Johnson County.