Columns: State (class) | Vacator | Reason for change | Successor | Date of successors formal installation
Virginia (1) | Vacant | Failure to elect | Isaac S. Pennybacker ( D ) | Elected December 3, 1845 | Massachusetts (2) | Isaac C. Bates ( W ) | Died March 16, 1845 | John Davis ( W ) | Elected March 24, 1845 | New Hampshire (2) | Benning W. Jenness ( D ) | Resigned June 13, 1846 after successor elected | Joseph Cilley ( D ) | Elected June 13, 1846 | South Carolina (3) | George McDuffie ( D ) | Resigned August 17, 1846 | Andrew Butler ( D ) | Elected December 4, 1846 | Iowa (2) | Iowa admitted to the Union December 28, 1846 | Iowa admitted to the Union December 28, 1846 | Vacant | Not filled this term | Iowa (3) | Iowa admitted to the Union December 28, 1846 | Iowa admitted to the Union December 28, 1846 | Vacant | Not filled this term | Louisiana (2) | Alexander Barrow ( W ) | Died December 29, 1846 | Pierre Soulé ( D ) | Elected January 21, 1847