There were few Irish migrants within the Confederate army.
There is not equivalent to the Union’s Irish Brigade. “The Confederate Irish
Brigade” is only a regiment, the 5th Missouri Infantry under the
command of Colonel Joseph Kelly, which saw action primarily in the
trans-Mississippi Theatre of the war.
The Hibernian Society, an Irish social group, in Charleston had engaged in drills and militia work since the 1790s. They were part of the 28th Regiment of South Carolina Militia and had seen action in the War of 1812, the Seminole War, and the Mexican War. By the time of the Civil War, the Irish Volunteers enlisted as a unit and became a company of the 1St South Carolina Volunteer Regiment
The regiment often associated with the Battle of Fredericksburg and helping create the mythology of Irish vs Irish was the 24th Georgia Volunteer Regiment, at the time under the command of Thomas Reade Rootes Cobb. Recruited in White, Banks, Towns, Rabun, Gwinnett, Elbert, Hall, Franklin, and Habersham counties, the regiment saw action primarily in Virginia as part of James Longstreet’s command within the Army of Northern Virginia. Only one company, Irish-born Robert McMillan’s Guard from Habersham county were predominately Irish.