Columns: District | Vacator | Reason for change | Successor | Date successor seated
Colorado Territory At-large | New seat | New seat | Hiram P. Bennett (Conservative R) | August 19, 1861 | Nevada Territory At-large | New seat | New seat | John Cradlebaugh | December 2, 1861 | Dakota Territory At-large | New seat | New seat | John B. S. Todd (D) | December 9, 1861 | Louisiana 1st | Vacant | Vacant | Benjamin F. Flanders (U) | December 3, 1862 | Louisiana 2nd | Vacant | Vacant | Michael Hahn (U) | December 3, 1862 | Virginia 1st | Vacant | Vacant | Joseph E. Segar (U) | May 6, 1862 | Virginia 7th | Vacant | Vacant | Charles H. Upton (U) | July 4, 1861 | Ohio 13th | John Sherman (R) | Resigned March 12, 1861 when elected U.S. Senator | Samuel T. Worcester (R) | July 4, 1861 | Pennsylvania 12th | George W. Scranton (R) | Died March 24, 1861 | Hendrick B. Wright (D) | July 4, 1861 | Oregon At-large | Andrew J. Thayer (D) | Election was successfully contested July 30, 1861 | George K. Shiel (D) | July 30, 1861 | Massachusetts 5th | William Appleton (CU) | Resigned September 27, 1861 due to failing health | Samuel Hooper (R) | December 2, 1861 | Kentucky 1st | Henry C. Burnett (D) | Expelled December 3, 1861 for support of secession | Samuel L. Casey (U) | March 10, 1862 | Kentucky 2nd | James S. Jackson (U) | Resigned December 13, 1861 to enter the Union Army | George H. Yeaman (U) | December 1, 1862 | Virginia 7th | Charles H. Upton (U) | Declared not entitled to seat February 27, 1862 | Lewis McKenzie (U) | February 16, 1863 | Illinois 9th | John A. Logan (D) | Resigned April 2, 1862 to enter the Union Army | William J. Allen (D) | June 2, 1862 | Pennsylvania 7th | Thomas B. Cooper (D) | Died April 4, 1862 | John D. Stiles (D) | June 3, 1862 | Massachusetts 9th | Goldsmith F. Bailey (R) | Died May 8, 1862 | Amasa Walker (R) | December 1, 1862 | Missouri 1st | Francis P. Blair, Jr. (R) | Resigned July 1862 to become colonel in Union Army | Vacant | Vacant for remainder of term