The Seventy-Third Infantry was recruited from the counties of Adams, Champaign, Christian, Hancock, Jackson, Logan, Piatt, Pike, Sangamon, Tazewell and Vermilion. It was mustered into the service at Camp Butler, August 21, 1862, and numbered nine hundred strong. It moved almost immediately for the front, Colonel Jaquess commanding. It reached Louisville, August 25.

Camp Jaquess was the first resting place of the Regiment in Kentucky. The first move of the Regiment after reaching Louisville was to Camp Yates. The Seventy-third was first brigaded with the Thirty-fourth and One Hundredth Illinois Infantry and the Seventy-ninth and Eighty-eighth Indiana. It bore its part in covering the retreat of the forces which had been defeated in an engagement at Richmond, Ky.; also in the movement by rail from Louisville to Cincinnati and Covington to assist in resisting an invasion by Kirby Smith's forces. The Regiment had acquired such proficiency in the simpler evolution of the drill that in marching through Cincinnati spectators were surprised to any learn it was not an old Regiment. Smith's invasion not materializing to any great extent the Seventy-third with other forces returned from Covington to Louisville the latter part of September.

A re-organization of the army placed the Seventy-third in a brigade with the Forty-fourth Illinois and the Second and Fifteenth Missouri. This brigade, under Colonel Leibold, Second Missouri, was assigned to Sheridan's Division, and remained in it until Sheridan was ordered East in the spring of 1864. October 1, 1862, the army under Buell started in pursuit of Bragg. On the 8th of that month military operations in Kentucky culminated in the battle of Perryville. A little after noon on this date the Seventy-third was posted in an exposed position, one within easy range of a Confederate battery. The withdrawal of the Regiment to the main line in an opportune moment no doubt saved it from severe loss. At about 3 o'clock P.M., the Seventy-third became engaged and so continued until after 4 o'clock, delivering and receiving a heavy fire. This battle over and Bragg getting off with his army and supplies, the Union army pursuing only as far as Crab Orchard, a change in the direction of the latter was ordered, and on November 7, it reached Nashville, Tenn. In the meantime Rosecrans had relieved Buell in command of the Army of the Cumberland. From the time the Regiment left Kentucky up and subsequent to the movement on Murfreesboro, it lost a number of men by disability and from disease; quite a number died at Bowling Green and many more at Nashville. The Regiment broke camp December 25, preparatory to moving on Stone River. The brigade, which at Mill Creek had been placed under the command of General Schafer, did not participate in any of the preliminary skirmishing at Stone River. On December 31, however, opportunity was afforded for every regiment to bear a part. General Schafer was killed before noon. Colonel Jaquess was with his Regiment at Perryville but was not at Stone River, so the Seventy-third was commanded by Major William Resson. During the day the Regiment was in several severe conflicts and fully established its reputation for courage. It was in the opening of the campaign against Tullahoma and Chattanooga, to which points Braggs forces had retreated. June 23, 1863, was the date on which the summer campaign was actively initiated on the part of the Infantry. At Fairfield and Estill Springs the Seventy-third was present but was not called into action. Crossing Elk River, the first stop was at Cowan Station. After a few days rest the Division proceeded through Cumberland Tunnel to Stevenson, Ala., where it remained until September 2; thence it moved to Bridgeport, and crossing the Tennessee River joined in the movement on Alpine, which flanked the enemy out of Chattanooga. The next hard marching was in the concentration of the Federal forces to meet those of the enemy at Chickamauga. Colonel Leibold was in command of the Brigade and Colonel Jaquess of the Regiment. The terrible strain of this memorable battle being over, the remnants of regiments and brigades fell back to Chattanooga. From the latter part of September to the 24th of November the Union forces were organizing and preparing for the brilliant achievements at Lookout Mountain and Missionary Ridge.

Missionary Ridge was the theater of operation for the Seventy-third in the conflict in November 1863. In this engagement the conduct of the Regiment fully merited the praise bestowed in congratulatory orders. Next came the campaign into East Tennessee to the relief of Burnside. Dandridge was visited by the Seventy-third and other regiments. This campaign was characterized by hard, slavish marching, and scant rations, East Tennessee having been redeemed, the Union army returned to Chattanooga; the Seventy-third encamping at Cleveland. May 3, 1864, the Atlanta campaign opened. The re-organization of the army after Chickamauga, placed the Regiment in First Brigade, Second Division, Fourth Corps. In vicinity of Catoosa Springs, the whiz of the enemy's bullets was first heard. At Rocky Faced Ridge, was treated to some of same kind of music. No chance to reciprocate at either of these two places, but at the latter some sharp-shooters, specially detailed from the Regiment, did good work. Some skirmishing near Dalton, and between there and Resaca. May 14, participated in battle of Resaca. May 17, Regiment bore a part in the action at Adairsville; and two days later in skirmishes about Kingston. At latter place, two or three days rest were obtained. Starting forward again, and coming in contact with the enemy, the month of June 1864, chronicled the following engagements, in most of which the Seventy-third participated: Burnt Hickory, Pine and Lost Mountains, New Hope Church and Kenesaw Mountain. In the assault on Kenesaw Mountain the Regiment suffered comparatively little, owing to the nature of ground. Was under fire July 4, 1864; on man killed. Reached Chattahoochie River about July 6, encamping above Vining's Station. July 9, made an expedition to Roswell, the seat of cotton factories, which were destroyed. Returned to Vining's Station, July 12. Crossed Chattahoochie River, July 13. One week later, participated in battle of Peach Tree Creek. Next came the skirmishing, the slow advances and delays, necessary to the siege or investment of Atlanta. The enemy evacuating and retreating from Atlanta, the engagements at Jonesboro and Lovejoy's Station occurred. In neither of these was the Regiment actively engaged, though under fire in both. Arrived at Atlanta, Sept. 8. About September 20th, the Fourth Corps returned by rail to Chattanooga. Made reconnoissance in force to Alpine Valley; returned to Chattanooga; thence by rail to Huntsville, Alabama. Then came the hard marching and the race with Hood's army for Nashville. Bore a part in the skirmishing near Columbia, Tennessee, south of Duck River, and crossed said river the night of November 28. Since starting out in May, the Brigade had three or four different commanders, including Leibold, F. Sherman and N. Kimball. It was now under Emerson Opedycke, Colonel One Hundred and Twenty-fifth Ohio. From Duck River, the Brigade fell back to Spring Hill, and being pressed by the enemy, skirmished a good part of the way. Participated in the action at Spring Hill, the afternoon of November 29. Stood picket that night, as on the previous night at Duck River. With the break of day, November 30, trouble commenced. Being already deployed, the Brigade skirmished nearly the whole distance from Spring Hill to Franklin. Arriving within one mile and a half of Franklin, Brigade was relieved from skirmish line, and marched directly into suburbs of town, passing on the way troops posted in front of, and also those occupying the works, and halted in position behind Carter's Hill. Fortunate, indeed, was it for the Union forces that a Brigade was posted there. At a critical moment - a crisis in the battle - this Brigade was thrust into the "imminent and deadly breach", and undoubtedly averted an overwhelming disaster. At the point of the bayonet, the breach was repaired, and the line of battle maintained unbroken until late at night, although the enemy repeatedly dashed wildly and furiously against it. Withdrawing from Franklin, and crossed the Harpeth, Nashville was reached December 1, 1864, about 1 o'clock P.M. With Opedycke's Brigade, or part of it, here was two nights' picketing in succession, in face of the enemy, nearly two days' skirmishing, participation in two battles, and the falling back from Duck River to Nashville, without any sleep that was at all restful. The Seventy-third took part both day (December 15 and 16, 1864), in battles at Nashville, in afternoon of 16th making, with many other regiments, its last bayonet charge, which was successful. Joined in pursuit of Hood, going to Pulaski, Tenn., at which place, about December 23, 1864, was last exposed to the enemy's fire. Proceeded to Huntsville, Alabama, arriving January 5, 1865. March 28, 1865, went by rail to Blue Springs, East Tennessee, remaining there until receiving orders to return to Nashville. Was mustered out of service at Nashville, June 12, 1865, and a few days later went to Springfield, Ill., on the same train with the Seventy-ninth Illinois, to receive pay and final discharge.

The following table shows the engagements in which the Regiment participated, as well as the casualties in each:

Each of the fifty-two officers and men represented in first column was killed outright. Of the forty-five who died of wound, fully one-third died the same day, or within twenty-four hours from time wounds were received. On the sixty-seven wounded who survived, the larger number were discharged. Many suffered amputation of either an arm, leg or foot.

In addition to the battles named, the Regiment actively participated in the following named actions: Pine Mountain, Lost Mountain, New Hope Church, Marietta, Jonesboro, Lovejoy Station and Spring Hill. In these actions the greater number of the fifty-nine wounded, "battle not stated", received those wounds. Quite a number of officers were slightly wounded, in many cases the wound not sufficiently serious to necessitate leaving the field or skirmish line.