The ten companies comprising the 53rd Pennsylvania rendezvoused at Camp Curtin in the fall of 1861. Company I, which the current 53rd portrays, was from Juniata County, the men taking the name "The Union Guards." Other companies hailed from Montgomery, Blair, Centre, Clearfield, Union, Carbon, Luzerne, Potter, Northumberland, Huntington and Westmoreland counties. The regiment was organized in early November 1861. Colonel John R. Brooke, a prominent Montgomery countian, was the unit's commander.
When the Army of the Potomac was organized, the 53rd was assigned to the First Division, Second Army Corps, where it remained during its entire term of service. After the siege of Yorktown, the 53rd first encountered the rebels at Fair Oaks on June 1, 1862, where the 53rd suffered almost a hundred casualties. During the Seven Days campaign , the regiment was lightly engaged. When the army moved north, the Second Corps was the last to leave the Peninsula and thus missed the Second Manassas campaign.
At Antietam on September 17, the 53rd covered the right flank of the division as it attacked the Sunken Road. In the final battle action of 1862, at Fredericksburg on December 13, the 53rd took 314 officers and men into one of the charges on the enemy position at Marye's Heights. Casualties numbered 21 killed, 133 wounded, and one missing, for a total of 155 or 49% of those engaged.
After wintering near Falmouth, the regiment took part in the Chancellorsville campaign, escaping with the loss of a mere eleven men. The 53rd then marched north to the fight in the Wheatfield at Gettysburg on July 2. As the division entered the field, only seven companies of the 53rd were in line, the other three serving as provost guards. Of the 135 soldiers who participated in the charge across the Wheatfield into the Rose Woods, eighty became casualties. Following the Bristoe Station and Mine Run campaigns that Fall, the remnant of the 53rd went into winter camp. Over the winter most of the survivors reenlisted for another three years and the regiment was granted a veterans furlough late in December 1863.
When the strengthened regiment returned to the Army of the Potomac, it took part in Grant's 1864 Virginia campaign, fighting in the Wilderness (May 5-6). At Spotsylvania, the 53rd was part of the May 12th Second Corps charge on the Mule Shoe salient. During the intense fighting in this battle, the regiment suffered 177 casualties. After being lightly engaged at the North Anna River, the regiment fought at Cold Harbor on June 3, where 69 officers and men were added to the casualty list. Then the 53rd took part in the initial assaults on the Petersburg defenses, losing 99 additional soldiers. During the ensuing siege of Petersburg, the 53rd fought at Ream's Station on August 25th, as well as numerous smaller engagements as Grant tightened the vise on Robert E. Lee's Confederates. The regiment fought at the White Oak Road on March 25, 1865, then at Farmville on April 6.
Following Lee's surrender, the 53rd returned to Washington, took part in the Grand Review on May 23, then was mustered out of service on June 30. During its four years of hard service, the 53rd Pennsylvania enrolled 1,993 officers and men. Of these, 200 were killed or mortally wounded. Another 587 were wounded but survived, and 194 soldiers died of disease, in Southern prisons, or from accidents.