1820.Successor later re-elected in the April 1821 election to the next term, see below. | nowrap | |- ! | James Johnson | | Democratic-Republican | 1813 | | Incumbent resigned when appointed as collector of customs in Norfolk.New member elected sometime in 1820.Democratic-Republican hold.Successor seated November 13, 1820.Successor later lost re-election in the April 1821 election to the next term, see below. | nowrap | |- ! | Tunstall Quarles | | Democratic-Republican | 1816 | | Incumbent resigned June 15, 1820.New member elected August 7, 1820.Democratic-Republican hold.Successor was also elected to the next term, see below.Successor seated November 13, 1820. | nowrap | |- ! | David Walker | | Democratic-Republican | 1816 | | Incumbent died March 1, 1820.New member elected August 7, 1820.Democratic-Republican hold.Successor was also elected to the next term, see below.Successor seated November 13, 1820. | nowrap | |- ! | Edward Dowse | | Democratic-Republican | 1818 | | Incumbent resigned.New member elected August 21, 1820.Democratic-Republican hold.Successor later re-elected in the November 6, 1820, election to the next term, see below.Successor seated November 13, 1820. | nowrap | |- ! | David Fullerton | | Democratic-Republican | 1818 | | Incumbent resigned May 15, 1820.New member elected October 10, 1820.Federalist gain.Successor was not a candidate in the same day's election for the next term, see below.Successor seated November 13, 1820. | nowrap | |- ! | Jonathan Mason | | Federalist | 1817 | | Incumbent resigned May 15, 1820, to pursue his law practice.New member elected on the second ballot November 6, 1820.Democratic-Republican gain.Successor also elected the same day to the next term, see below.Successor seated November 27, 1820. | nowrap | |- ! | John Holmes | | Democratic-Republican | 1816 | | Incumbent's seat moved from but incumbent resigned when elected U.S. Senator.New member elected November 7, 1820.Federalist gain.Successor also elected the same day in the to the next term, see below.Successor seated December 11, 1820. | nowrap | |- ! | Zabdiel Sampson | | Democratic-Republican | 1817 | | Incumbent resigned July 26, 1820.New member elected November 24, 1820 on the second ballot.Successor seated December 18, 1820.Successor was already elected to the next term, see below. | nowrap | |- ! | Joseph Hiester | | Democratic-Republican | 17981804 1814 | | Incumbent resigned in December 1820 when elected Governor of Pennsylvania.New member elected December 10, 1820.Democratic-Republican hold.Successor