The 23rd Regiment Illinois Volunteer Infantry, known as the "First Irish" or "Irish 'Brigade'", was an infantry

Infantry

Infantrymen are soldiers who are specifically trained for the role of fighting on foot to engage the enemy face to face and have historically borne the brunt of the casualties of combat in wars. As the oldest branch of combat arms, they are the backbone of armies...

 regiment

Regiment

A regiment is a major tactical military unit, composed of variable numbers of batteries, squadrons or battalions, commanded by a colonel or lieutenant colonel...

 that served in the Union Army

Union Army

The Union Army was the land force that fought for the Union during the American Civil War. It was also known as the Federal Army, the U.S. Army, the Northern Army and the National Army...

 during the American Civil War

American Civil War

The American Civil War was a civil war fought in the United States of America. In response to the election of Abraham Lincoln as President of the United States, 11 southern slave states declared their secession from the United States and formed the Confederate States of America ; the other 25...

.

Service

The 23rd Illinois Infantry was organized at Chicago, Illinois and mustered into Federal service on June 15, 1861.

The regiment was mustered out on July 24, 1865.

Total strength and casualties

The regiment suffered 4 officers and 50 enlisted men who were killed in action or who died of their wounds and 2 officers and 93 enlisted men who died of disease, for a total of 149 fatalities.

Commanders

• Colonel
  Colonel
  Colonel , abbreviated Col or COL, is a military rank of a senior commissioned officer. It or a corresponding rank exists in most armies and in many air forces; the naval equivalent rank is generally "Captain". It is also used in some police forces and other paramilitary rank structures...
  
   James A. Mulligan
  James A. Mulligan
  James A. Mulligan was colonel of the 23rd Illinois Volunteer Infantry Regiment in the Union Army during the American Civil War. On February 20, 1865, the United States Senate confirmed the posthumous award to Colonel Mulligan of the rank of brevet brigadier general of U.S...
  
   - killed in action July 24, 1864.
• Lieutenant Colonel
  Lieutenant colonel
  Lieutenant colonel is a rank of commissioned officer in the armies and most marine forces and some air forces of the world, typically ranking above a major and below a colonel. The rank of lieutenant colonel is often shortened to simply "colonel" in conversation and in unofficial correspondence...
  
  Samuel Simison - mustered out with the regiment.