James Adelbert Mulligan (June 30, 1830 – July 26, 1864) was colonel of the 23rd Illinois Volunteer Infantry Regiment in the Union Army during the American Civil War.

[2] At the onset of the Civil War, Mulligan raised the 23rd Illinois Volunteer Infantry Regiment in 1861, which was locally known as the "Irish Brigade" (not to be confused with a New York unit by the same name).

Price was reportedly so impressed by Mulligan's demeanor and conduct during and after the battle that he offered him his own horse and buggy, and ordered him safely escorted to Union lines.

Mulligan may have been a poor administrator, but unlike some later commandants, he had made efforts to improve conditions at the camp which were hampered by an inadequate budget and bureaucratic indifference.

Mulligan was told to expect no help whatsoever; he was to hold as long as possible, then conduct a fighting retreat as slowly as possible to cover the other withdrawing Union units.

[14] Mulligan led his minuscule force out of their trenches after Johnson's initial charge, driving the attackers back upon the divisions of Generals Robert Rodes and Stephen D. Ramseur.

Although the outcome of the battle was a foregone conclusion, Mulligan managed to hold Early's main force at Leestown for the entire day before being compelled to give way—albeit very slowly.

Mulligan continued to battle Early all the way from Leestown to Martinsburg, Virginia, buying valuable time for Union commanders to concentrate their forces in the Valley.

Mulligan briefly held off Gordon's units, but Confederate Maj. Gen. John C. Breckinridge led a devastating flank attack against the Irishmen from the east side of the Valley Pike.

As he stood up in his saddle to spur his men on, Southern sharpshooters concealed in a nearby stream bed managed to hit the Union commander.