Following the Union defeat at the Battle of Second Manassas (Bull Run), Maj. Gen. John Pope’s Army of Virginia (AV), with attached units of the Army of the Potomac (AP), retreated to the fortified heights of Centreville. Gen. Robert E. Lee, commanding the Army of Northern Virginia (ANV), sought a decisive battle to destroy Pope’s army but determined to avoid attacking him in the Centreville fortifications. Consequently, Lee ordered Stonewall Jackson’s force of about 17,000 troops to flank the Federals by marching around Centreville via the Little River Turnpike (today’s Rt. 50) toward Fairfax Court House. A successful flanking movement would place Confederate forces directly in Pope’s rear and render the Union position at Centreville untenable.
By noon on September 1, Gen. Pope realized his precarious position. With Braddock Road occupied by Banks’ II Corps (AV) guarding wagon trains, Pope’s only line of retreat was the Fairfax-Centreville road (today’s Rt. 29). That road converged with the Little River Turnpike near Jermantown just west of Fairfax. If Jackson’s column reached Jermantown first, Pope’s line of retreat would be cut. Pope had no choice but to abandon Centreville and withdraw his army to Jermantown and Fairfax C. H. Pope at once ordered McDowell’s III Corps (AV) to Jermantown to occupy a line near Difficult Run so as to protect the Centreville road and the Union line of retreat.
Around 1:00 p.m., Pope ordered Maj. Gen. Joseph Hooker to proceed immediately to Jermantown and take command of all troops there and at Fairfax C. H. At the same time, Pope ordered Brig. Gen. Isaac Stevens’ and Maj. Gen. Jesse Reno’s divisions of IX Corps (AP), about 4,000 troops, to move across-country to the Little River Turnpike (near Ox Hill) and there take position to check Jackson’s advance. This move would delay the Confederates long enough for Gen. Hooker to organize a stronger defensive force behind Difficult Run near Jermantown. Among the withdrawing Union corps, Heintzelman’s III Corps (AP) with Kearny’s division, was ordered to support Stevens and Reno from their position on the Fairfax-Centreville Road (Rt. 29).
However, Jackson’s forces reached Ox Hill first, and as Stevens’ division crossed the elevated ground near the Millan house (just south of Ox Hill), the soldiers could see a line of Jackson’s skirmishers advancing across open fields toward them. These skirmishers were guarding Jackson’s flank, but to Stevens, they portended a Confederate attack upon the retreating Union columns moving toward Fairfax. Without hesitation, Stevens determined to attack, threw out his own skirmishers, and hastened his troops forward to meet Jackson.
By 4:30 p.m. Stevens had formed his three brigades into battle lines while his artillery pounded the woods near the turnpike. Under fire, Jackson hurried to meet this unexpected attack. A.P. Hill’s division deployed along the wood line on north side of a large cornfield. Ewell’s (Lawton’s) division deployed in the woods on Hill’s left, and Jackson’s (Starke’s) division extended the line through thick woods east of Ox Road.
At this point, Gen. Stevens ordered his division forward and they advanced up the slope until about 200 yards from the wood line when blasts of musketry from Ewell’s (Lawton’s) division staggered the ranks. Even as men fell, Stevens’ lines of battle continued to press onward as the general extended his line into the cornfield on the left. Now a withering fire brought the line nearly to a standstill. Determined to move the attack forward, Stevens seized the colors of the 79th New York, and with the uplifted flag, rallied his men and renewed the attack. The whole line responded and followed their general, charging up the slope toward the woods and into the cornfield on the left. Near the wood line Stevens was shot and killed but his lead regiments surged over the fence into the woods and drove the rebels before them. At the height of the attack a violent thunderstorm erupted with continuous lightning flashes, deafening thunder, and torrents of rain. Stevens’ success was short-lived, for while his soldiers routed some of Ewell’s (Lawton’s) regiments at the fence line, they were soon driven out of the woods by counter-attacking troops of Early’s brigade. Concurrently the disjoined advance of Reno’s 21st Massachusetts in the woods on Stevens’ right ended in a bloody mauling and a precipitous retreat.
Now, Maj. Gen. Philip Kearny’s division arrived on the scene (responding to Stevens’ earlier plea for support) and Kearny ordered his lead brigade, some 2,000 troops of Brig. Gen. David Birney, into the fields and woods on Stevens’ left (north of the Reid house). There they attacked two of A.P. Hill’s brigades (Branch and Pender) on the right of Jackson’s line. With wet ammunition and fixed bayonets, Birney’s brigade battled Hill’s North Carolinians in the cornfield and adjacent woods until a bayonet charge by three of Birney’s regiments closed the action. During this time, Kearny rode east in the gloomy mist looking for reinforcements to support Birney’s right flank and found the battered 21st Massachusetts. Leading them north into the cornfield, Kearny was shot and killed by Georgia skirmishers. In the dim light, the Georgians mingled with the Massachusetts men and the fighting quickly became a hand-to-hand brawl using bayonets and swinging muskets. Now dark, the fighting ceased and the exhausted soldiers finally withdrew. Gen. Robinson’s and Col. Poe’s brigades of Kearny’s division held the Union line until early morning. Around 3:00 a.m., the Federals fell back and continued their retreat to Fairfax, leaving the battlefield to the Confederates.
More than 1,500 casualties resulted from this confused and bloody encounter that continued for two hours in rain, storm and darkness. Among the dead were Union Generals Stevens and Kearny. The Battle of Ox Hill (Chantilly) ended Lee’s Northern Virginia Campaign, but the battle was a stalemate. In two concentrated attacks, some 6,000 Union soldiers had battled to a standstill a Confederate force of about 17,000 troops, of whom perhaps 10,000 were engaged. In the end, the Confederates possessed the battlefield, but Stevens and Kearny had successfully thwarted Jackson’s flanking movement and defended Pope’s line of retreat. The next day, Pope’s army withdrew to the fortifications of Washington.
On September 3, the Army of Northern Virginia marched to Dranesville and thence to Leesburg and the Potomac River fords. Crossing the river on September 4-7, Lee’s army entered Maryland. On September 5, Maj. Gen. George McClellan again assumed command of Union forces. On September 17, the two armies would clash again near Antietam Creek, at Sharpsburg, Maryland.