I haven't found the song, but I found this information:

Thomas William Sweeny ("Fightin' Tom") (1820 – 1892) was an American soldier who served in the Mexican-American War and then was a general in the Union Army during the American Civil War. Sweeny was born at Cork, Ireland.... In 1866, he commanded the ill-fated Fenian invasion of Canada, after which he was arrested for breaking neutrality laws between the United States and Britain, but was soon released.