| nowrap | James M. Mason (D) | Expelled March 28, 1861, for supporting the rebellion.Successor was elected. | nowrap | Waitman T. Willey (U) | July 9, 1861 |- | Illinois (2) | nowrap | Stephen A. Douglas (D) | Died June 3, 1861.Successor was appointed. | nowrap | Orville H. Browning (R) | June 26, 1861 |- | Texas (2) | nowrap | John Hemphill (D) | Expelled sometime in July 1861. | colspan=2 | Vacant thereafter |- | Illinois (2) | nowrap | Orville H. Browning (R) | Interim appointee lost election to finish the term.Successor elected January 12, 1863. | nowrap | William A. Richardson (D) | January 30, 1863 |- | Arkansas (2) | nowrap | William K. Sebastian (D) | Expelled July 11, 1861. | colspan=2 | Vacant thereafter |- | Arkansas (3) | nowrap | Charles B. Mitchel (D) | Expelled July 11, 1861. | colspan=2 | Vacant thereafter |- | Michigan (2) | nowrap | Kinsley S. Bingham (R) | Died October 5, 1861.Successor was elected. | nowrap | Jacob M. Howard (R) | January 17, 1862 |- | Oregon (2) | nowrap | Edward D. Baker (R) | Killed at Battle of Ball's Bluff October 21, 1861.Successor was appointed. | nowrap | Benjamin Stark (D) | October 29, 1861 |- | Kentucky (3) | nowrap | John C. Breckinridge (D) | Expelled December 4, 1861, for supporting the rebellion.Successor was elected. | nowrap | Garrett Davis (U) | December 23, 1861 |- | Missouri (1) | nowrap | Trusten Polk (D) | Expelled January 10, 1862, for supporting the rebellion.Successor was appointed. | nowrap | John B. Henderson (U) | January 17, 1862 |- | Missouri (3) | nowrap | Waldo P. Johnson (D) | Expelled January 10, 1862, for disloyalty to the government.Successor was appointed. | nowrap | Robert Wilson (U) | January 17, 1862 |- | Indiana (1) | nowrap | Jesse D. Bright (D) | Expelled February 5, 1862, on charges of disloyalty.Successor was appointed. | nowrap | Joseph A. Wright (U) | February 24, 1862 |- | Tennessee (1) | nowrap | Andrew Johnson (D) | Resigned March 4, 1862. | colspan=2 | Vacant thereafter |- | Rhode Island (1) | nowrap | James F. Simmons (R) | Resigned August 15, 1862.Successor was elected. | nowrap | Samuel G. Arnold (R) | December 1, 1862 |- |