The 42nd Regiment Illinois Volunteer Infantry was an infantry regiment that served in the Union Army during the American Civil War.

Flotilla Brigade, Army of Mississippi, to April, 1862.

1st Brigade, 13th Division, Army of the Ohio, to November, 1862.

3rd Brigade, 2nd Division, 4th Army Corps to June, 1865.

2nd Brigade, 2nd Division, 4th Army Corps, to August, 1865.

March to St. Charles, Mo., thence moved to Fort Holt, Ky., February 2–20, 1862.

Duty along line of Memphis and Charleston R. R. till September 2.

Repulse of Forest's attack on Edgefield November 5.

Occupation of Middle Tennessee till August 16.

Passage of Cumberland Mountains and Tennessee River and Chickamauga, Ga. Campaign August 16-September 22.

March to relief of Knoxville, Tenn., and Campaign in East Tennessee November 28, 1863, to January 15, 1864.

Operations on line of Pumpkin Vine Creek and battles about Dallas, New Hope Church and Allatoona Hills May 25-June 5.

Operations about Marietta and against Kenesaw Mountain June 10-July 2.

Ruff's Station Smyrna, Camp Ground, July 4.

Moved to New Orleans, La., June 15–18, thence to Fort Lavacca, Texas, July 18–23, thence to Camp Irwin and duty there till August 17.

Post duty at Port Lavacca till December.

Mustered out at Camp Irwin December 16 and discharged at Springfield, Ill., January 10, 1866.

[1] The regiment suffered 13 officers and 168 enlisted men who were killed in action or mortally wounded and 5 officers and 201 enlisted men who died of disease, for a total of 387 fatalities.

[3] There is a monument to the 42nd Illinois Infantry at Chickamauga and Chattanooga National Military Park.