The ‘Federal Retreat’ wayside marker is on the east side of the driveway to the Thomas farm on the north side of Baker Valley Road about 0.3 mile southwest of Araby Church Road. A small parking area next to the driveway is the trailhead for the Thomas Farm walking tour. (39.35707° N, 77.390764° W; map)

Two other markers, Thomas Farm and Thick of the Battle, are next to this marker.

Federal Retreat wayside marker at Monocacy

Federal Retreat marker (click to enlarge)

From the marker:

Federal Retreat

4:30-5:00 p.m. July 9, 1864

The Northerners held, then lost, then retook the Thomas house grounds as the fighting ebbed and flowed in the stifling heat. Casualties mounted quickly on both sides. Union Maj. Gen. Lew Wallace could see that his numbers were dwindling and that the Confederates were coming in waves. Wallace gave the order to retreat.

“Under a raking of fire of both musketry and artillery,” his troops pulled back and fled to the northeast past Gambrill Mill to the road to Baltimore. The Confederates had won the battle, but the Union had won a critical one-day delay in Lt. Gen. Jubal A. Early’s attempted raid on Washington.

From the sidebar:

Total Casualties
Estimates vary greatly for troops and casualties in the Battle of Monocacy. The Union had approximately 5,800 men and suffered 1,294 killed, wounded, or missing. The Confederates had 15,000 to 16,000 troops and 700 to 900 casualities.

The wayside markers on the Thomas farm at Monocacy.

The wayside markers on the Thomas farm at Monocacy.