In the tenth district, Republican Senator Charles Leopold Matthies died on October 16, 1868, causing a vacancy in his seat.

[10] In the eighteenth district, Republican Senator John R. Needham died on July 9, 1868, causing a vacancy in his seat.

[11] In the twenty-fourth district, Republican Senator William Penn Wolf resigned on March 3, 1869, causing a vacancy in his seat.

To claim control of the chamber from Republicans, the Democrats needed to net 18 Senate seats.

[b] Source:[16] District boundaries were redrawn before the 1869 general election for the Iowa Senate: