Columns: State (class) | Vacator | Reason for change | Successor | Date of successors formal installation
New Hampshire (2) | Vacant | Legislature failed to elect on time. | John Parker Hale (R) | July 30, 1855 | Alabama (3) | Vacant | Legislature failed to elect on time. | Benjamin Fitzpatrick (D) | November 26, 1855 | Pennsylvania (3) | Vacant | Legislature failed to elect on time. | William Bigler (D) | January 14, 1856 | California (3) | Vacant | Legislature failed to elect on time. | William M. Gwin (D) | January 13, 1857 | Indiana (3) | Vacant | Legislature failed to elect on time. | Graham N. Fitch (D) | February 4, 1857