The marker for Brooks’ Brigade of Smith’s Division is on the north side of Richardson Avenue, east of Mumma’s Lane. (Sharpsburg Pike tour map) The brigade was better known as the Vermont Brigade, which is honored by a nearby monument. 

From the marker:

U.S.A.
Sixth Army Corps

Brooks’ Brigade, Smith’s Division

Brig. Gen. W.T.H. Brooks, Commanding.

Organization.

2d, 3d, 4th, 5th and 6th Vermont Infantry

September 17, 1862.

Brooks’ Brigade left its camp in Pleasant Valley at 6 A.M. of the 17th, crossed the Antietam at Pry’s Ford and reached the field about noon. It was ordered to the support of Sedgwick’s Division, Second Corps, on the Union right but, before getting into position, was ordered to the support of French’s Division and formed in Mumma’s Cornfield, on ground vacated by the 14th Connecticut, its left connecting with French, its right resting on Mumma’s Lane, facing south parallel to and about 170 yards from the Bloody Lane.

It was subjected to a galling fire of both Artillery and Sharpshooters, causing some loss.

It remained in this position until the morning of the 19th.

No. 73.