- Dec 7 Sylvester Churchill, US Union brigadier general, dies
- Dec 13 Conrad Feger Jackson, US Union brigadier general, dies in Battle of Fredericksburg at 49
- Dec 13 Maxcy Gregg, American Brigadier General (Confederate Army), dies in Battle of Fredericksburg at 48
- Dec 13 Thomas Reade Rootes Cobb, Brigadier General (Confederate Army), dies in Battle of Fredericksburg at 39
- Dec 14 George Dashiell Bayard, Union Brigadier General, dies at 27
- Dec 18 Johnson Kelly Duncan, American architect and Confederate brig-general, dies at 35 of malarial fever
- Dec 20 Robert Knox Scottish surgeon, anatomist and zoologist
- Dec 24 Joseph Funk, early American composer, dies at 84
- Dec 28 Joaquim Casimiro Jr., Portuguese composer, dies at 54
- Dec 31 James Edward Rains, American lawyer and Brigadier General (Confederate Army), dies in Battle of Stone's River at 29
- Dec 31 Joshua Woodrow Sill, US Union brigadier general, dies in Battle of Stone's River at 31