His regiment was among the troops defending Harpers Ferry against Joseph B. Kershaw's Confederate brigade of Maj. Gen. Lafayette McLaws's division during the Maryland Campaign.

He was severely wounded with a gunshot through his lower jaw in fighting on Maryland Heights during the Battle of Harpers Ferry.

He commanded the 3rd Brigade, 3rd Division, II Corps, after Col. George L. Willard's death on July 2, 1863, at the Battle of Gettysburg.

Sherrill, in his first full day commanding the brigade, was positioned near Ziegler's Grove on Cemetery Ridge, when he was mortally wounded on July 3 by a musket shot in the bowels.

Lt. Col. James M. Bull, 126th New York Infantry, who filed the brigade's report, giving a detailed account of the artillery barrage on July 3 but not much on the repulse of Pickett's Charge, places Sherrill's death at 4 p.m.[3] His granddaughter, Carrie Babcock Sherman, was Second Lady of the United States, 1909-1912.