Mea culpa. I believed Wikipedia.

Wikipedia said that the 123rd Volunteer Illinois Regiment was at the Battle of Stones River, and I didn't think to double check.

The battle was December 31, 1862 to January 2, 1863, and at that time the Regiment was chasing the raider John Morgan (not our ancestor) through Tennessee, and were in the general area but not at the battle. John Morgan (yes, our Morgan ancestor from Coles County, Illinois, later Salt Lake City) was a member of the 123rd, and several years ago I listed the battle among his service. I will correct that.

Here is a detailed description of the actions of the 123rd Regiment.

123rd Regiment, Illinois Infantry 

OVERVIEW: Organized at Mattoon, Ill., and mustered in September 6, 1862. Left State for Louisville, Ky., September 19, 1862. Attached to 33rd Brigade, 10th Division, Army of the Ohio, to October, 1862. 33rd Brigade, 10th Division, 1st Corps, Army of the Ohio, to November, 1862. 1st Brigade, 5th Division, Centre 14th Army Corps, Army of the Cumberland, to January, 1863. 1st Brigade, 5th Division, 14th Army Corps, to June, 1863. 1st Brigade, 4th Division, 14th Army Corps, to October, 1863. 3rd Brigade, 2nd Division, Cavalry Corps, Army of the Cumberland, to November, 1864, and Military Division Mississippi, to June, 1865. 

SERVICE: Duty at Louisville, Ky., till October 1, 1862. Pursuit of Bragg into Kentucky October 1-12. Battle of Perryville, Ky., October 8. March to Munfordsville October 12-18, and duty there till November 30. Expedition to Cave City October 31-November 26. Moved to Bledsoe Creek November 30. Pursuit of Morgan to Bear Wallow December 26, 1862, to January 2, 1863. March to Nashville, thence to Murfreesboro, Tenn., January 3-10, 1863. Duty at Murfreesboro till June. Action at Woodbury January 24. Expedition to Auburn, Liberty and Alexandria February 3-5. Cainsville February 15. Expedition to Woodbury March 3-8. Breed's Hill March 4. Vaught's Hill, near Milton, March 20. Expedition to Lebanon, Carthage and Liberty April 1-8. Expedition to McMinnville April 20-30. Regiment mounted and armed with Spencer carbines May 6. Attached to Wilder's Mounted Brigade, Smithville, June 5. Middle Tennessee (or Tullahoma) Campaign June 24-July 7. Big Spring Branch June 24. Hoover's Gap June 24-26. Occupation of Manchester June 27. Estill Springs July 2. Occupation of Middle Tennessee till August 16. Expedition to Columbia and Centreville July. Expedition from Decherd, Tenn., August 5-9. Passage of the Cumberland Mountains and Tennessee River and Chickamauga (Ga.) Campaign August 16-September 22. Ringgold, Ga., September 11. Lee and Gordon's Mills September 11-13. Leet's Tan Yard (or Rock Springs) September 12-13. Alexander and Reed's Bridges September 18. Pea Vine Creek September 18. Crawfish Springs and Dyer's Ford September 18. Battle of Chickamauga September 19-21. Operations against Wheeler and Roddy September 30-October 17. Hill's Gap, Thompson's Cove, near Beersheeba, October 3. Murfreesboro Road October 4. Near McMinnville October 4-5. Farmington October 7. Sim's Farm, near Shelbyville, October 7. Camp at Maysville, Ala., October 19-December 21. Moved to Pulaski December 21, thence to Mooresville, Ala., January 12, 1864, and guard Tennessee River till April. Moved to Columbia, Tenn., thence to join army near Dalton, Ga., reporting May 11. Atlanta (Ga.) Campaign May 11-September 8. Battle of Resaca May 13-15. Near Dallas May 24. Operations on Pumpkin Vine Creek and battles about Dallas, New Hope Church and Allatoona Hills May 25-June 5. Near Big Shanty June 9. Operations about Marietta and against Kenesaw Mountain June 10-July 2. Noonday Creek June 19. Powder Springs, Lattimer's Mills, Noonday Creek, June 20. Noonday Creek and assault on Kenesaw June 27. Nickajack Creek July 2-5. Rottenwood Creek July 4. Chattahoochie River June 5-17. Stone Mountain Station July 19. Garrard's Raid to Oxford and Covington July 22-24. Garrard's Raid to South River July 27-31. Snapfinger Creek July 27. Flat Rock Bridge July 28. Siege of Atlanta August 1-13. Operations about Chattahoochie River Bridge, Pace's and Turner's Ferries August 26-September 2. Occupation of Atlanta September 2. Operations against Hood in North Georgia and North Alabama September 29-November 3. Near Lost Mountain October 4-7. New Hope Church October 7. Dallas October 7. Rome October 10-11. Narrows October 11. Coosaville Road, near Rome, October 13. Near Summerville October 18. Little River October 20. Leesburg, Blue Pond, October 21. Ladiga, Terrapin Creek, October 28. Dismounted November 1, and ordered to Louisville, Ky. Refitting at Louisville till December 28. Moved to Gravelly Springs, Ala., December 28, 1864-January 20, 1865. Wilson's Raid on Selma, Ala., and Macon, Ga., March 22-April 24. Selma April 2. Montgomery April 12. Columbus, Ga., April 16. Macon, Ga., April 20. Moved to Chattanooga, Tenn., May 23; thence to Nashville and duty there till June 27. Mustered out June 27 and discharged at Springfield, Ill., July 11, 1865. 

Regiment lost during service 3 Officers and 82 Enlisted men killed and mortally wounded and 1 Officer and 133 Enlisted men by disease. Total 219.

(The original source for this list seems to be Frederick H. Dyer, A Compendium of the War of the Rebellion (Des Moines, Iowa: Dyer Publishing Company, 1908), 1098.)