100th Illinois Infantry

100th Illinois Infantry
Unit name	100th Illinois Infantry
Dates	August 1862 – June 1865
Allegiance	Union
Branch	Infantry
Size	Regiment
Garrison	Chicago, Illinois
Notable commanders	Major General John A. Logan

100th Illinois Infantry was a Union volunteer regiment raised in Illinois during the American Civil War that served in the Western Theater, participating in campaigns and battles across Missouri, Kentucky, Tennessee, and the Mississippi River corridor. Organized amid the strategic demands following Confederate operations in the Trans-Mississippi Theater and the Vicksburg Campaign, the regiment contributed to riverine operations, siege actions, and pursuit operations under army commands including the Army of the Tennessee and corps commanded by leaders such as William T. Sherman and Ulysses S. Grant. The unit’s service intersected with major events like the Siege of Vicksburg and the Atlanta Campaign, reflecting Illinois’s role in Union mobilization and Western operations.

Formation and Organization

The regiment was mustered in at Chicago and other Illinois rendezvous points during August 1862 under state militia authority and federal mustering directed by the Adjutant General of Illinois. Recruitment drew volunteers from counties such as Cook County, Illinois, Will County, Illinois, and Kane County, Illinois, with companies organized under captains commissioned by Governor Richard Yates. Training and initial drilling occurred at state camps influenced by regulations from the United States War Department and doctrine practiced in training depots like those used by regiments assigned to the Department of the Missouri. The regiment’s muster rolls, officers’ commissions, and ordnance issues followed standards overseen by the Quartermaster General of the United States Army.

Service History

Upon federal induction, the regiment was assigned to operations in the Western Theater and attached to brigades within divisions of the Army of the Tennessee and subordinate commands. In late 1862 the unit participated in operations designed to secure lines of communication along the Mississippi River and to counter Confederate cavalry raids led by figures such as Nathan Bedford Forrest and John Hunt Morgan. Throughout 1863 the regiment took part in siege operations and riverine expeditions connected to the Vicksburg Campaign and coordinated with naval forces of the United States Navy under flag officers who supported joint operations on inland waters. During 1864 the regiment joined larger maneuver campaigns including elements of the Atlanta Campaign that were conducted by armies commanded by William T. Sherman and subordinate generals such as Henry W. Halleck’s earlier staff influences on Western operations. The regiment’s final months included occupation and garrison duty in captured territory and participation in pursuit operations during the closing Appalachian and Gulf Coast campaigns.

Engagements and Campaigns

The regiment saw action in engagements and operations associated with the Siege of Vicksburg, riverine assaults along the Mississippi River, and expeditions into Confederate-held Kentucky and Tennessee. It was engaged in skirmishes and battles connected to the strategic effort to control the Mississippi River and cut the Confederacy in two, interacting operationally with forces at Jackson, Mississippi and engaging enemy detachments tied to the defense of regional rail hubs such as Meridian, Mississippi. During the 1864 campaigns the regiment participated in actions related to the Atlanta Campaign and operations around key rail centers like Kennesaw Mountain and Decatur, Georgia, as well as in pursuit phases that intersected with maneuvers toward Savannah, Georgia and the Carolina Campaign.

Commanders and Notable Personnel

Regimental leadership included field officers commissioned in Illinois service with ties to state political figures such as Governor Richard Yates and congressional advocates of enlistment in the United States Congress. Officers and noncommissioned leaders transitioned between regimental command and brigade staff assignments under corps commanders including John A. Logan and division leaders aligned with William T. Sherman’s operational plan. Enlisted men included volunteers who later gained recognition in veterans’ organizations like the Grand Army of the Republic and who testified before wartime and postwar inquiries involving commanders from the Western Theater. Several members advanced to positions in Illinois state government, municipal office in Chicago, or in railroad administration during the postwar Reconstruction era.

Casualties and Strength

Muster strength varied through the regiment’s service owing to recruitment, attrition, and reenlistment; initial strength approximated regimental norms for Union volunteer infantry with ten companies of roughly 100 men each, adjusted by casualties and detachments. The regiment sustained losses from combat, disease, and accidents consistent with Western Theater regiments—engaging enemy forces affiliated with Confederate commands such as those led by Jefferson Davis’s strategic directives and suffering disease outbreaks common in campaign environments referenced in reports to the Surgeon General of the United States Army. Official returns recorded killed, wounded, missing, and disease casualties that influenced subsequent consolidation and veteran furloughs authorized by the War Department.

Legacy and Commemoration

Veterans of the regiment participated in postwar commemoration through reunions, monument dedications at national and state battlefield parks, and membership in organizations such as the Grand Army of the Republic and state-level associations that influenced memorial projects in Springfield, Illinois and Chicago. Regimental histories and veterans’ letters contributed to archival collections in repositories like the Illinois State Historical Library and influenced monument placement at sites associated with the Vicksburg National Military Park and other Western Theater memorials. The regiment’s service informed Illinois’s Civil War memory in works by historians of the American Civil War and in centennial and sesquicentennial commemorations sponsored by state historical societies and municipal heritage programs.

Category:Units and formations of the Union Army from Illinois