The new American Party, based on the nativist "Know Nothing" movement characterized by opposition to immigration and anti-Catholicism, gained six seats.

Elections were held August 4, 1845, after the March 4, 1845 beginning of the term, but before the House first convened in December 1845.

Elections were held April 7, 1845, after the March 4, 1845 beginning of the term, but before the House first convened in December 1845.

Elections were held August 4, 1845, after the March 4, 1845 beginning of the term, but before the House first convened in December 1845.

Maryland's October 1, 1845 elections were after the March 4, 1845 beginning of the new term, but still before the Congress convened in December 1845.

Elections were held November 3–4, 1845, after the March 4, 1845 beginning of the term, but before the House first convened in December 1845.

Elections were held April 2, 1845, after the March 4, 1845 beginning of the term, but before the House first convened in December 1845.

Elections were held April 24, 1845, after the March 4, 1845 beginning of the term, but before the House first convened in December 1845.