123rd Illinois Volunteer Infantry Regiment The 123rd Illinois Volunteer Infantry Regiment was an infantry regiment that served in the Union Army during the American Civil War . In 1863 and 1864 it was temporarily known as the Mounted Infantry , 123rd Regiment . Background . This regiment was organized at Camp Terry , Mattoon , Coles County , Illinois by Colonel James Monroe , who at the time was major of the 7th Illinois Infantry . Companies A , C , D , H , I and K were from Coles County ; B from Cumberland ; E from Clark ; F and G from Clark and Crawford . As a colonel in 1861 , Ulysses S . Grant organized his first command , the 21st Illinois Volunteer Infantry Regiment , in Mattoon . It was mustered into service on September 6 , 1862 , with James Monroe as Colonel , Jonathan Biggs , of Westfield , Clark County , as Lieutenant Colonel , and James A . Connolly , of Charleston , Illinois , as Major . On the 19th of September 1862 , the Regiment was loaded into freight cars at Mattoon , and transported to Louisville , Kentucky , where it was at once put to work , under Major General William " Bull " Nelson , to fortify the city against Confederate General Braxton Bragg , who was then advancing on it in pursuit of Union General Don Carlos Buell . On October 1 , having been assigned to the Thirty - third Brigade ( General William R . Terrill ) , Fourth Division ( General James S . Jackson ) , in McCook ' s Corps , the regiment started on the march under Buell , southward through Kentucky , after Bragg , who had turned back , and up to this time the regiment never had battalion drill , and hardly an attempt at company drill , as all the officers , except the colonel , were " raw recruits " . Just 19 days after leaving Mattoon , the regiment engaged in the Battle of Perryville , where 36 men were killed in action and 180 wounded . Generals Terrill and Jackson were both killed immediately behind and within twenty feet of the line of the regiment . Among the wounded were Captain Coblentz of Company E , First Lieutenant S . M . Shepard of Company A and Adjutant L . H . Haslin . Following the devastating bloodshed the 123rd was assigned to protect the railroad bridge across the Green River at Munfordville , Kentucky in November and December 1862 . It has become known as the " Battle for the Bridge , " which began when the Union garrison led by John T . Wilder , prior to his assuming command of the 123rd , surrendered during the Battle of Munfordville . The 123rd was initially assigned to the Army of the Ohio from September 1862 to November 1862 , and then to the Army of the Cumberland from November 1862 to June 1865 . The commanding general of the Army of the Cumberland was William Rosecrans . The regiment was in the 1st Brigade with Colonel Albert S . Hall , which was part of the Fifth Division commanded by Brigadier General Joseph J . Reynolds , reporting to Major General George Henry Thomas . Later , for a time , the 123rd Illinois Infantry Regiment was attached to the mounted unit known as the " Wilder Lightning Brigade " commanded by Wilder . It was assigned to the 1st Brigade , 4th Division , 14th Army Corps . The regiment was mounted from May 1863 to November 1864 . Spencer carbines , invented by Christopher Spencer , were introduced at this time . In combat , the carbines , shorter and lighter than the rifle version , were first used in the Battle of Hoover ' s Gap . During the Battle of Selma , First Lieutenant O . J . McManus , Sergeants J . S . Mullen and Henry E . Cross , Corporal McMurry and Privates Daniel Cook , John Bowman , Marion White and Henry Woodruff were killed , with 50 wounded , including Lieutenant Colonel Biggs , Adjutant L . B . Bane , Captains W . E . Adams and Owen Wiley , Lieutenants Alex . McNutt and J . R . Harding . Late in the war , the regiment pursued Confederate General John Bell Hood . The unit was instrumental in the capture of former Confederate capital Montgomery , Alabama . In June 1865 new recruits and some veterans were transferred to the 61st Regiment as the 123rd prepared to disband . Those who remained were mustered out June 27 , 1865 by Captain L . M . Hosea and formally discharged at Springfield , Illinois on July 11 , 1865 . Total strength and casualties . The regiment lost during service three officers and 82 enlisted men killed and mortally wounded and one officer and 133 enlisted men by disease for a total of 219 . Commanders . Colonel James Monroe : September 6 , 1862 - October 7 , 1863 ( killed at the Battle of Farmington ) < BR > Brigadier General of Volunteers James S . Jackson : October 1 , 1862 - October 8 , 1862 ( killed at the Battle of Perryville ) < BR > Brigadier General of Volunteers William R . Terrill : September 9 , 1862 - October 8 , 1862 ( killed at the Battle of Perryville ) < BR > Lt . Colonel James A . Connolly < BR > Captain Oscar R . Bane < BR > Colonel John T . Wilder : May 6 , 1863 - November 1864 ( resignation ) < BR > Brigadier General Kenner Garrard : May 20 , 1864 - October 28 , 1864 < BR > Major General James H . Wilson : October 28 , 1864 - June 27 , 1865 Infantry men . John Hamilton Morgan Sources . James Austin Connolly ( Major , 123rd Illinois ) , " Three Years in the Army of the Cumberland : The Letters and Diary of Major James A . Connolly " , ed . Paul M . Angle ( 1928 ; reprint , Indiana University Press , 1996 ) , ISBN 978 - 0 - 253 - 21073 - 9 . < BR > Thomas Lawrence Connelly . " Autumn of Glory : The Army of Tennessee , 1862 - 1865 " . LSU Press . ISBN 0 - 8071 - 2738 - 8