Of the one-hundred and forty-eight citizens of Mansfield who served during the Civil War, forty-one of them saw action with the 21^st. The 21^st volunteer infantry was commissioned on September 5^th, 1862 with a complement of 965 recruits, a number that would later swell to 1,023. After brief and uneventful tours with the 9^th Corps, and the 7^th Corps, the 21^st regiment first saw significant action with the 18^th Corps.

On May 16^th, 1864 the 21^st Regiment occupied the right side of the Union line during the Battle of Drewry’s Bluff. Several hours of hard fighting ensued when Confederate forces attacked under the cover of heavy fog in an effort to capture a railroad line linking Richmond and Petersburg. Unable to hold against the Confederate advance, the 21^st Regiment and other elements of the 1^st Division were forced to retreat and relinquish the railroad to the Confederate forces. The 21^st regiment sustained its heaviest losses of the war during this battle with 79 wounded, 23 captured, and 16 killed including one Mansfield citizen. 

Following the retreat from Drewry’s Bluff, the 21^st traveled to White House Landing where it would support the Army of the Potomac in several engagements near Cold Harbor beginning on May 29^th and running through June 9^th. After the evacuation of Cold Harbor, a large Union force including the 21^st regiment advanced on Petersburg. After supporting an initial charge against the Confederate lines on June 17^th, the 21^st regiment was relegated to a reserve role, and performed picket and skirmish duties for the next 3 weeks. During this time a total of 49 casualties were incurred.

The battle at Petersburg proved to be the final major engagement for the 21^st Infantry Regiment during the war. After Petersburg, the regiment participated in a raid on Fredricksburg on March 4^th 1865 intended to curb the trade of tobacco for supplies by the Confederate Army. The 21^st was among the first infantry troops to enter Richmond on April 3, 1865.
The service of the 21^st Connecticut Volunteer Infantry in the Union Army was officially ended on June 16^th 1865. A week later the regiment arrived home in New Haven before later attending a celebration at the State House in Hartford. All members of the 21^st regiment were finally discharged and the regiment formally was disbanded on July 6^th 1865.