Reacting to Early's raid, Union General-in-Chief Lt. Gen. Ulysses S. Grant dispatched two brigades of the VI Corps, about 5,000 men, under Brig. Gen.James B. Ricketts on July 6, 1864. Until those troops arrived, however, the only Federal army between Early and the capital city was a ragtag group of 2,300 mostly Hundred Days Men commanded by Lew Wallace. At the time, Wallace, who would eventually become best known for his book Ben-Hur: A Tale of the Christ, was the head of the Union's Middle Atlantic Department, headquartered at Baltimore. Very few of Wallace's men had ever seen battle.
Agents of the Baltimore and Ohio Railroad reported signs of Early's advance on June 29; this intelligence and subsequent reports were passed to Wallace by John W. Garrett, the president of the railroad and a Union supporter. Uncertain whether Baltimore or Washington, D.C. was the Confederate objective, Wallace knew he had to delay their approach until reinforcements could reach either city.
At Frederick, following the Battle of Frederick in which Confederate cavalry drove Union units from the town, Early demanded, and received, $200,000 ransom to forestall his destruction of the city. Frederick Junction, also called Monocacy Junction, three miles southeast of Frederick, was the logical point of defense for both cities. The Georgetown Pike to Washington and the National Road to Baltimore both crossed the Monocacy River there as did the Baltimore and Ohio Railroad. If Wallace could stretch his little army over six miles of riverfront to protect both turnpike bridges, the railroad bridge, and several fords, he could make Early disclose the strength and objective of the Confederate force and delay him as long as possible.
Wallace's prospects brightened with word that the first contingent of VI Corps troops commanded by General Ricketts, had reached Baltimore and were rushing by rail to join Wallace at the Monocacy. On Saturday, July 9, combined forces of Wallace and Ricketts, numbering about 5,800, were positioned at the bridges and fords of the river. The higher elevation of the river's east bank formed a natural breastwork for some of the soldiers. Others occupied two block-houses, the trenches they had dug with a few available tools, or what cover they could find among the fences and crops of once peaceful farms.
Confederate Maj. Gen. Dodson Ramseur's division encountered Wallace's troops on the Georgetown Pike near the Best Farm; Maj. Gen. Robert E. Rodes's division clashed with the Federals on the National Road. Believing that a frontal attack across the Monocacy would be too costly, Early sent John McCausland's cavalry down Buckeystown Road to find a ford and outflank the Union line. Confederates penetrated the Monocacy defenses below the McKinney-Worthington Ford and attacked Wallace's left flank. Some of the heaviest fighting that day took place where they confronted Ricketts's veterans at a fence separating the Worthington and Thomas farms.
The Federals fought fiercely to hold position, but it was only a matter of time before the superior force—about 14,000 Confederates—gained control. A three-pronged attack from Maj. Gen. John B. Gordon's division pushed Ricketts back toward the National Road where he was joined by the beleaguered troops who had fought Ramseur and Rodes all day.
By late afternoon the Federals, following the northernmost Confederate victory of the war, were retreating toward Baltimore, leaving behind over 1,294 dead, wounded, and captured. Later, General Wallace gave orders to collect the bodies of the dead in a burial ground on the battlefield where he proposed a monument to read: "These men died to save the National Capital, and they did save it."
The way lay open to Washington. Early's army had won the field at Monocacy, but at the expense of 700 to 900 killed and wounded and at least one day lost. The next morning the Confederates marched on, and by midday Monday, Early stood inside the District of Columbia at Fort Stevens. Early could see the Capitol Dome through his glasses. But with his troops spread out far behind him and seeing the impressive Fort Stevens, decided not to attack. However there were artillery exchanges and skirmishes that day, July 11, 1864, and the following day. On July 13 Early retraced his steps and crossed the Potomac back into Virginia at White's Ferry.
Monocacy cost Early a day's march and his chance to capture Washington. Thwarted in the attempt to take the capital, the Confederates turned back to Virginia, ending their last campaign to carry the war into the North.
General Early wrote in a report of the 1864 campaign:
Some of the Northern papers stated that, between Saturday and Monday, I could have entered the city; but on Saturday I was fighting at Monocacy, thirty-five miles from Washington, a force which I could not leave in my rear; and after disposing of that force and moving as rapidly as it was possible for me to move, I did not arrive in front of the fortifications until after noon on Monday, and then my troops were exhausted ...
General Grant also assessed Wallace's delaying tactics at Monocacy:
If Early had been but one day earlier, he might have entered the capital before the arrival of the reinforcements I had sent .... General Wallace contributed on this occasion by the defeat of the troops under him, a greater benefit to the cause than often falls to the lot of a commander of an equal force to render by means of a victory.
The battlefield remained in private hands for over 100 years before portions were acquired in the late 1970s to create the Monocacy National Battlefield.