|- | | nowrap | George W. Scranton (R) | Died March 24, 1861. | nowrap | Hendrick B. Wright (D) | July 4, 1861 |- | | nowrap | Charles F. Adams Sr. (R) | Resigned May 1, 1861, to become Ambassador to Great Britain. | nowrap | Benjamin Thomas (U) | June 11, 1861 |- | | nowrap | Edward Joy Morris (R) | Resigned June 8, 1861, to become Minister Resident to Turkey. | nowrap | Charles J. Biddle (D) | July 2, 1861 |- | | nowrap | John S. Carlile (U) | Resigned July 9, 1861, to become United States Senator from the loyal faction of Virginia. | nowrap | Jacob B. Blair (U) | December 2, 1861 |- | | nowrap | John Bullock Clark (D) | Expelled July 13, 1861, for having taken up arms against the Union. | nowrap | William A. Hall (D) | January 20, 1862 |- | | nowrap | Andrew J. Thayer (D) | Election was successfully contested July 30, 1861. | nowrap | George K. Shiel (D) | July 30, 1861 |- | | nowrap | John W. Reid (D) | Withdrew August 3, 1861, and then expelled December 2, 1861, for having taken up arms against the Union. | nowrap | Thomas L. Price (D) | January 21, 1862 |- | | nowrap | Samuel Curtis (R) | Resigned August 4, 1861, to become colonel of the 2nd Iowa Infantry. | nowrap | James F. Wilson (R) | October 8, 1861 |- | | nowrap | William Appleton (CU) | Resigned September 27, 1861, due to failing health. | nowrap | Samuel Hooper (R) | December 2, 1861 |- | | nowrap | John A. McClernand (D) | Resigned October 28, 1861, to accept a commission as brigadier general of volunteers for service in the Civil War. | nowrap | Anthony L. Knapp (D) | December 12, 1861 |- | | nowrap | Henry C. Burnett (D) | Expelled December 3, 1861, for support of secession. | nowrap | Samuel L. Casey (U) | March 10, 1862 |- | | nowrap | James S. Jackson (U) | Resigned December 13, 1861, to enter the Union Army. | nowrap | George H. Yeaman (U) | December 1, 1862 |- | | nowrap | Charles H. Upton (U) | Declared not entitled to seat February 27, 1862. |