Commanded by Brigadier General Abner Doubleday (1)
| First Brigade | Colonel Walter Phelps, Jr. | |
| 22nd New York Infantry Regiment | Lieutenant Colonel John McKie, Jr. | |
| 24th New York Infantry Regiment | Captain John D. O’Brian (w) | |
| 30th New York Infantry Regiment | Colonel William M. Searing | |
| 84th New York Infantry Regiment (14th Militia) | Major William H. de Bevoise | |
| 2nd United States Sharpshooters Regiment | Colonel Henry A. V. Post (w) | |
| Second Brigade | Lieutenant Colonel J. William Hofmann | |
| 7th Indiana Infantry Regiment | Major Ira G. Grover | |
| 76th New York Infantry Regiment | Captain John W. Young (2) | |
| 95th New York Infantry Regiment | Major Edward Pye | |
| 56th Pennsylvania Infantry Regiment | Captain Frederick Williams | |
| Third Brigade | Brigadier General Marsena R. Patrick | |
| 21st New York Infantry Regiment | Colonel William F. Rogers | |
| 23rd New York Infantry Regiment | Colonel Henry C. Hoffman | |
| 35th New York Infantry Regiment | Colonel Newton B. Lord | |
| 80th New York Infantry Regiment (20th Militia) | Lieutenant Colonel Theodore B. Gates | |
| Fourth Brigade | Brigadier General John Gibbon | |
| 19th Indiana Infantry Regiment | Lieutenant Colonel Alois O. Bachman (3)(k) Captain William W. Dudley |
|
| 2nd Wisconsin Infantry Regiment | Lieutenant Colonel Thomas S. Allen (w) Captain George B. Ely |
|
| 6th Wisconsin Infantry Regiment | Lieutenant Colonel Edward S. Bragg (w) Major Rufus R. Dawes |
|
| 7th Wisconsin Infantry Regiment | Captain John B. Callis | |
| Artillery | Captain John Albert Monroe | |
| 1st Battery New Hampshire Light Artillery | Lieutenant Frederick M. Edgell | |
| 1st New York Light Artillery, Battery L | Captain John A. Reynolds | |
| Rhode Island Light Artillery, Battery A | Captain John Albert Monro | |
| 4th United States Artillery, Battery B | Captain Joseph B. Campbell (w) Lieutenant James Stewart |
Key to notes:
(k) = killed, (w) = wounded, (mw) = mortally wounded, (c) = captured
Links for regiments, batteries, companies, and individuals go to unit histories or biographies on www.civilwarintheeast.com
Notes:
(1) Took command after Brigadier General John P. Hatch was wounded on 9/14 at South Mountain
(2) Took command after Colonel William P. Wainwright was wounded on 9/14 at South Mountain
(2) Took command after Colonel Solomon Meredith stepped down as disabled on the 16th, having been injured when his horse fell on him at Second Bull Run along with “subsequent fatigue and exposure of the marches” since then