The marker for Anderson’s Brigade of Meade’s Division is on the north side of Mansfield Avenue, north of the North Woods. (Mansfield Avenue tour map)

Anderson's Brigade, Meade's Division, marker 24 of the War Department Union markers at Antietam

From the marker:

U.S.A.
First Army Corps

Anderson’s Brigade, Meade’s Division

Lieut. Col. Robert Anderson, 9th Penna. Reserve, Commanding.

Organization.
9th Pennsylvania Reserves
10th Pennsylvania Reserves
11th Pennsylvania Reserves
12th Pennsylvania Reserves

(September 17, 1862.)  

Anderson’s Brigade advanced from this point about 6:30 A.M. in support of Gibbon’s, Phelps’ and Patrick’s Brigades of Doubleday’s Division, midway between the North Woods and the D. R. Miller house, the 10th Regiment was sent to the west about 700 yards to protect the flank of the Union line against a threatened advance of the enemy. The three remaining Regiments became engaged with the enemy in the north edge of the Cornfield south of the Miller house.

No. 24.

Anderson's Brigade, Meade's Division, marker 24 of the War Department Union markers at Antietam