It was extremely close during CWI, as well. Fielded regular units to both sides of the conflict, as well as the infamous Guerillas.
A Union state that had the western tier of counties vacated by general order in an attempt to defuse the border war...
My great-great-grandfather (brother of the aforementioned Confederate) was in his 40s during the war and had a large family but eventually spent 6 months in a Union outfit--he had moved to the far southwestern part of the state before the war. He named a daughter after a Union general.
A more distant relative died in the battle of Wilson's Creek--on the Confederate side.