23rd Illinois Volunteer Infantry Regiment The 23rd Regiment Illinois Volunteer Infantry , known as the " First Irish " or " Irish ' Brigade ' " , was an infantry regiment that served in the Union Army during the American Civil War . The 23rd Illinois Infantry was organized at Chicago , Illinois and mustered into Federal service on June 15 , 1861 . Initially assigned to garrison the town of Lexington , Missouri , the regiment surrendered to a much larger force of pro - secession Missouri State Guard commanded by State Guard Major General Sterling Price at the First Battle of Lexington in September 1861 . After being paroled , General John C . Fremont ( commanding the Department of Missouri ) had the 23rd Illinois mustered out of service , but in December General George McClellan ( now supreme commander in chief of all Union armies ) had it restored . After being reconstituted , the regiment left camp in the spring of 1862 for western Virginia , where it spent most of the rest of the war stationed there . In 1864 , it joined General Philip Sheridan ' s army in the Valley Campaign . At the end of the year , the 23rd headed to the Richmond area for the Siege of Petersburg and was present at Appomattox . The regiment was mustered out on July 24 , 1865 . Service . Organized at Chicago , Ill . , and mustered in June 15 , 1861 . Moved to Quincy , Ill . , July 14 , thence to St . Louis , Mo . , and to Jefferson City July 21 , and duty there until September 8 . March to Lexington September 8 – 11 . Siege of Lexington September 12 – 20 . Captured by Price September 20 and paroled . Regiment mustered out by order of General Fremont October 8 , 1861 , but restored by order of General McClellan , December 10 , 1861 . Reassembled at Chicago and guard prisoners at Camp Douglas until June 14 , 1862 . Moved to Harper ' s Ferry , West Va . , June 14 . Attached to R . R . District , Mountain Department , Harper ' s Ferry and New Creek to July , 1862 . R . R . District , 8th Army Corps , Middle Department , to September , 1862 . R . R . District West Va . to January , 1863 . New Creek , Va . , Defenses Upper Potomac , 8th Army Corps , Middle Department , to March , 1863 . 5th Brigade , 1st Division , 8th Army Corps , to June , 1863 . Mulligan ' s Brigade , Scammon ' s Division Dept . of West Virginia to December , 1863 . 2nd Brigade , 2nd Division , West Virginia , to April , 1864 . Kelly ' s Command , Reserve Division , West Virginia , to July , 1864 . 1st Brigade , 3rd Infantry , Division West Virginia , to July , 1864 . 3rd Brigade , 1st Infantry Division , West Virginia , to December , 1864 . 2nd Brigade , Independent Division , 24th Army Corps , Army of the James , to June , 1865 . 1st Brigade , Independent Division , 24th Army Corps , to July , 1865 . Detailed Service ( after reconstitution ) . Duty at New Creek , West Va . , until April , 1863 . Relief of Clarksburg , W . Va . , September 1 , 1862 . Relief of Parkersburg September 3 . Action at Moorefield , South Fork of the Potomac , November 9 ( Cos . " B , " " D , " " K " ) . Relief of Colonel Washburn at Moorefield January 3 – 4 , 1863 . Moved to Grafton April 25 , 1863 . Skirmish at Greenland Gap April 25 ( Co . " G " ) . Phillippi April 26 . Altamont April 26 ( Detachment ) . Rowlesburg April 28 ( Cos . " B , " " F , " " I " ) . Fairmont April 29 ( Co . " K " ) . Pursuit of Lee July , 1863 . Hedgesville and Back Creek July 6 . At Petersburg , W . Va . , August 16 . Petersburg Gap September 4 . South Fork September 11 ( Co . " I " ) . Moorefield November 8 – 9 . Demonstration from Kanawha Valley , W . Va . , December 8 – 25 . Operations In Hampshire and Hardy Counties December 31 , 1863 , to January 5 , 1864 , and January 27 to February 7 . Medley January 29 – 30 . Regiment veteranize at New Creek April , 1864 , and on furlough until June . Scout to Moorefield February 21 – 22 ( Detachment ) . Raid on Baltimore & Ohio Railroad between Bloomfield and Piedmont May 5 ( Non - Veterans ) . Leetown July 3 . Operations about Harper ' s Ferry July 4 – 7 . Bolivar Heights July 4 – 6 . Maryland Heights July 6 – 7 . Snicker ' s Ferry July 17 – 18 and July 20 . Kernstown ( or Winchester ) July 24 . Medley July 30 . Sheridan ' s Shenandoah Valley Campaign August 7 to November 28 . Cedar Creek August 12 . Winchester August 17 . Halltown August 22 – 23 . Berryville September 3 . Battle of Winchester September 19 . Fisher ' s Hill September 22 . Duty In the Shenandoah Valley until December . Moved to Petersburg front December 30 . Siege operations against Petersburg and Richmond January to April , 1865 . Duty in trenches before Richmond and on the Bermuda Hundred front until March 27 . Moved to Hatcher ' s Run March 27 – 28 . Appomattox Campaign March 28 - April 9 . Hatcher ' s Run March 30 – 31 and April 1 . Assault on Fort Gregg and fall of Petersburg April 2 . Pursuit of Lee April 3 – 9 . Appomattox Court House April 9 . Surrender of Lee and his army . Duty in the Department of Virginia until July . Mustered out at Richmond , Va . , July 24 , and discharged at Chicago , Ill . , July 30 , 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 .