| Detail | Information |
|---|---|
| Full Name | James Adelbert Mulligan |
| Primary Role | Union Army colonel, 23rd Illinois Infantry |
| Key Event or Campaign | Defense of Lexington, Missouri, September 1861 |
| Time Period | American Civil War, 1861–1864 |
| Associated Location | Illinois and the Trans-Mississippi theater, United States |
Introduction
Colonel James A. Mulligan (1830–1864) was a Union volunteer officer best known for commanding the 23rd Illinois Infantry, a regiment drawn heavily from Chicago’s Irish community. A lawyer and local political figure before the Civil War, Mulligan became closely associated with the defense of key frontier positions in the Trans-Mississippi West and, later, with the hard fighting of the Army of West Virginia in the Shenandoah Valley. His stand at Lexington, Missouri, in 1861 and his death in action at the Second Battle of Kernstown in 1864 made him one of the more visible ethnic Irish officers in Union service. He matters historically as a representative figure in the use of state-raised ethnic regiments for strategically exposed garrison and holding duties during the war.
Historical Context
James A. Mulligan’s military career developed within the structures of the Union’s volunteer army system, where state governments organized regiments that were then mustered into federal service. Illinois, a rapidly growing Free State with strong Republican leadership, mobilized large numbers of volunteers early in the war. Many units were formed around ethnic, religious, or local identities to encourage enlistment and cohesion. Mulligan’s 23rd Illinois Infantry, sometimes known as the “Irish Brigade” of Chicago, reflected the intersection of immigrant community networks and state military administration.
The early war fighting in Missouri, where Mulligan first came to prominence, unfolded in the unsettled environment of a border slave state that remained in the Union but contained strong secessionist forces. Federal authorities sought to secure river routes, arsenals, and communication lines with limited regular troops, relying heavily on politically connected volunteer officers. Garrison commanders like Mulligan operated with constrained resources, improvised fortifications, and shifting local allegiances, facing opponents who combined secessionist state guards, irregular forces, and Confederate volunteers.
By 1864, when Mulligan served in the Shenandoah Valley, the Union war effort had moved toward coordinated campaigns under centralized command, but many volunteer colonels still held significant tactical responsibility in secondary theaters. The Valley was both a supply region for the Confederacy and a corridor threatening the North, making it a persistent focus of mid-level Union commanders whose units were repeatedly engaged, redeployed, and worn down.
Defining Action or Conflict
Mulligan’s most defining military action was his command of the Union garrison at Lexington, Missouri, in September 1861. Ordered to hold a river town of local and strategic importance, he commanded roughly 2,500–3,500 men, depending on the stage of the engagement, including elements of the 23rd Illinois and other units. Facing him was a much larger force of the pro-secession Missouri State Guard under Major General Sterling Price, whose numbers may have exceeded 10,000 when militia and irregulars are included.
Mulligan’s troops fortified the grounds of the Masonic College in Lexington, creating an entrenched position later known as “Mulligan’s Hill.” Over several days, Price’s forces gradually pressed in, cut Union access to the Missouri River, and restricted Mulligan’s water supply. The engagement became notable for the use of hemp bales by the Missouri State Guard. Soaked to reduce the risk of fire, these bales were rolled forward as movable breastworks, enabling Confederate-aligned troops to advance under cover toward Mulligan’s lines and close in on the defenses.
As ammunition and water ran low and no relief appeared, Mulligan’s command faced collapse. After prolonged resistance, he agreed to an unconditional surrender on 20 September 1861. The capitulation transferred control of Lexington and large quantities of arms and supplies to Price’s forces, while Mulligan and his men became prisoners of war, later paroled.
Though a tactical defeat for the Union, the defense drew northern attention. The length of resistance against a numerically superior force and the circumstances of the surrender underscored the vulnerability of isolated Union garrisons in contested border regions. Mulligan’s performance at Lexington, widely reported, shaped his subsequent military assignments and his reputation as a regimental and brigade-level commander.
Long-Term Impact
Mulligan’s later Civil War service and death in the Shenandoah Valley gave his earlier experience at Lexington a retrospective significance. After exchange and return to duty, he continued to command the 23rd Illinois and, at times, larger formations in the Department of West Virginia. At the Second Battle of Kernstown (24 July 1864), his brigade confronted Confederate forces under Lieutenant General Jubal Early. During the fighting he was mortally wounded while directing his troops, and he died a few days later.
From a military history perspective, Mulligan’s career illustrates how volunteer colonels could move from politically influenced appointments in frontier garrisons to front-line roles in major campaigns, while still operating within the limits of ad hoc logistics, variable training, and evolving command structures. His units were often used to hold exposed positions or delay larger enemy forces, tasks central to Union strategy but less visible than the operations of higher-ranking generals.
In later historical writing, Mulligan appears frequently in studies of Irish-American participation in the Union war effort, alongside more widely known Eastern theater Irish brigades. His leadership of the 23rd Illinois demonstrates how ethnic regiments functioned outside the main Virginia fronts, particularly in the Trans-Mississippi and in the interior border states. Locally, in Chicago and parts of Illinois, he became a reference point for commemorations of Irish Catholic military service. More broadly, he serves as a case study of mid-level command in a mass volunteer army, where tactical decisions at garrison and brigade level shaped outcomes in regions far from the principal theaters of war.
Conclusion
James A. Mulligan’s life bridged city politics in antebellum Chicago and the realities of volunteer command during the American Civil War. His conduct at Lexington, Missouri, demonstrated how state-raised ethnic regiments were used to hold contested ground with limited support, and his later service in the Shenandoah Valley showed the continued reliance on such officers in demanding field operations. His death in 1864 ended a career rooted in local networks but tied to broader federal military objectives. Historically, Mulligan stands as a representative Union colonel whose experiences clarify how the war was fought and sustained beyond the highest levels of command.