Civil War songs that touch on the war are obvious for the list, as WYSIWYG says, but all of the popular songs, composed or folk, secular and religious, were sung around the fires at night or while marching or waiting between marches. Some would have been put together many years before. Largely Irish units would sing songs of the auld sod along with the new ones that they were learning. Officers on leave would sing more sophisticated songs with families and friends. Irish Sergeant mentioned this, and I agree with his drift- where do you cut this off?

Early in this thread someone asked for the camp-meeting song whose tune was taken for John Brown's Body and The Battle Hymn. There is so much here that I don't know if he got an answer. It was composed by George Pullen Jackson of South Carolina, "Say, Brother, Will You Meet Us?" Rex posted the song in thread 20569: Say Brother