The marker for Gordon’s Brigade of William’s Division (marker 55) is on the east side of Hagerstown Pike, just south of Cornfield Avenue. (Philadelphia Brigade Park tour map) 
From the marker:
U.S.A.
Twelfth Army Corps
Gordon’s Brigade, William’s Division
Brig. Gen. George H. Gordon, Commanding.
Organization.
2nd Massachusetts Infantry,
3rd Wisconsin Infantry
27th Indiana Infantry
13th New Jersey Infantry
107th New York Infantry
Zouaves D’Afrique, Pennsylvania
September 17, 1862 No. 2.
Immediately after the withdrawl of Gordon’s Brigade to the East Woods, after being relieved by Sedgwick’s Division, it was ordered to the support of that Division in the West Woods.
The 13th New Jersey and 2nd Massachusetts advanced into this road – the former north and the latter south of this point – where they encountered such a destructive fire from the enemy that they were compelled to retire to the East Woods. Later in the day, the 13th New Jersey advanced into the woods west of the Dunkard Church and took position on the right of Greene’s Division.
No. 55