James Shields was an Irish American politician and United States Army officer, who is the only person in U.S. history to serve as a Senator for three different states, and one of only two to represent multiple states in the U.S. Senate. A member of the Democratic Party, Shields represented Illinois from 1849 to 1855, in the 31st, 32nd, and 33rd Congresses, Minnesota from 1858 to 1859, in the 35th Congress, and Missouri in 1879, in the 45th Congress.

The 31st United States Congress was a meeting of the legislative branch of the United States federal government, consisting of the United States Senate and the United States House of Representatives. It met in Washington, D.C., from March 4, 1849, to March 4, 1851, during the 16 months of the Zachary Taylor presidency and the first eight months of the administration of Millard Fillmore's. The apportionment of seats in this House of Representatives was based on the 1840 United States census. The Senate had a Democratic majority, while there was a Democratic plurality in the House.