In the ninth district, Republican Senator Alvin Saunders resigned on May 14, 1861, causing a vacancy in his seat.

[15] In the tenth district, Republican Senator James Falconer Wilson resigned on October 7, 1861, causing a vacancy in his seat.

In the fourteenth district, Democratic Senator Andrew Oliphant Patterson resigned on May 14, 1861, causing a vacancy in his seat.

[18] In the thirty-fifth district, Republican Senator Thomas Drummond resigned on May 14, 1861, causing a vacancy in his seat.

To claim control of the chamber from Republicans, the Democrats needed to net five Senate seats.