| Martin Jenkins Crawford | | Democratic | 1855 | Incumbent re-elected. | nowrap | |- ! | Robert Pleasant Trippe | | Know Nothing | 1855 | Incumbent re-elected. | nowrap | |- ! | Hiram B. Warner | | Democratic | 1855 | | Incumbent retired.New member elected.Democratic hold. | nowrap | |- ! | John Henry Lumpkin | | Democratic | 1855 | | Incumbent retired.New member elected.Democratic hold. | nowrap | |- ! | Howell Cobb | | Democratic | 18421851 1855 | | Incumbent retired.New member elected.Democratic hold. | nowrap | |- ! | Nathaniel Greene Foster | | Know Nothing | 1855 | bgcolor=lavender | Incumbent retired.New member elected.Know Nothing hold. | nowrap | |- ! | Alexander H. Stephens | | Democratic | 1843 | Incumbent re-elected. | nowrap | |} Illinois |- ! | Elihu B. Washburne | | Republican | 1852 | Incumbent re-elected. | nowrap | |- ! | James Hutchinson Woodworth | | Republican | 1854 | | Incumbent retired.New member elected.Republican hold. | nowrap | |- ! | Jesse O. Norton | | Republican | 1852 | | Incumbent retired.New member elected.Republican hold. | nowrap | |- ! | James Knox | | Republican | 1852 | | Incumbent retired.New member elected.Republican hold. | nowrap | |- ! | colspan=3 | Vacant | | Rep. William Alexander Richardson (D) resigned August 25, 1856, to run for governor of Illinois.New member elected.Democratic hold.Winner was not candidate for unexpired term, see above. | nowrap | |- ! | Thomas L. Harris | | Democratic | 18481850 1854 | Incumbent re-elected. | nowrap | |- ! | colspan=3 | Vacant | | Rep. James C. Allen (D) resigned July 18, 1856, amid election contest.New member elected.Democratic hold.Winner was not candidate for unexpired term, see above. | nowrap | |- ! | colspan=3 | Vacant | | Rep.-elect Lyman Trumbull (D) was later elected U.S. senator and took office March 4, 1855.New member elected.Democratic hold.Winner was not candidate for unexpired term, see above. | nowrap | |- ! | Samuel S. Marshall | | Democratic | 1854 | Incumbent re-elected. | nowrap | |} Indiana |- ! | Smith Miller | | Democratic | 1852 | | Incumbent retired.New member elected.Democratic hold. | nowrap | |- ! | William Hayden English | | Democratic | 1852 | Incumbent re-elected. | nowrap |