The 109th United States Congress began on January 3, 2005. There were nine new senators (two Democrats, seven Republicans) and 40 new representatives (16 Democrats, 24 Republicans) at the start of its first session. Additionally, one senator (a Democrat) and six representatives (two Democrats, four Republicans) took office on various dates in order to fill vacancies during the 109th Congress before it ended on January 3, 2007.
| State | Image | Senator | Took office | Switched party | Prior background | Birth year |
|---|---|---|---|---|---|---|
| New Jersey | 
|
Bob Menendez (D) | January 18, 2006 | No Appointed; replaced Jon Corzine (D) |
U.S. House of Representatives New Jersey Senate New Jersey General Assembly |
1954 |
| District | Delegate | Switched party | Prior background | Birth year |
|---|---|---|---|---|
| Puerto Rico at-large | Luis Fortuño (PNP/R) | Yes | Secretary of Economic Development and Commerce of Puerto Rico | 1960 |
| District | Representative | Took office | Switched party | Prior background | Birth year |
|---|---|---|---|---|---|
| California 5 | Doris Matsui (D) | March 10, 2005 | No | White House staffer | 1944 |
| Ohio 2 | Jean Schmidt (R) | September 6, 2005 | No | State Representative | 1951 |
| California 48 | John Campbell (R) | December 7, 2005 | No | State Senator | 1955 |
| California 50 | Brian Bilbray (R) | June 13, 2006 | No | U.S. House of Representatives | 1951 |
| New Jersey 13 | Albio Sires (D) | November 13, 2006 | No | State Assemblyman | 1951 |
| Texas 22 | Shelley Sekula-Gibbs (R) | November 13, 2006 | No | City Councilor | 1953 |
