(1803 - 1862)
Home State: Connecticut
Education: US Military Academy, West Point, NY, Class of 1822;Class Rank: 2
Command Billet: Army Corps Commander
Branch of Service: Infantry
Unit: Twelfth (XII) Army Corps
He graduated second in his Class from the US Military Academy at West Point in 1822, and was commissioned 2nd Lieutenant in the Corps of Engineers on 1 July 1822. He served on engineering boards and constructed and repaired coastal defenses. He was promoted First Lieutenant in 1832 and Captain in 1838. He was Chief Engineer under General Zachary Taylor in the Mexican War (1846-47), where he was brevetted Major (defense of Ft. Brown, TX) and was wounded in action at Monterey on 21 September 1846. He was again brevetted, to Lieutenant Colonel, for his actions there. He was honored by brevet a third time, to Colonel, for conduct at the battle of Buena Vista in February 1847. He then continued on engineering duties until 1853, when he was appointed staff Colonel in the Inspector General's Department, and served in California, Oregon, and Texas. On 14 May 1861 he was promoted to Brigadier General in the Regular Army and was given command of the Washington defenses.
On the Campaign
Mansfield was given command of the Federal Twelfth (XII) Army Corps on September 15 the first field command in his 40 year Army career. He was mortally wounded before 9am on the 17th while bringing up his troops near the Cornfield and died the next day at a field hospital on the Line farm. He was succeeded in command of the XII Corps by BGen A. Williams of his First Division.
He was one of the 6 General Officers killed or mortally wounded at Sharpsburg.
The rest of the War
He was (posthumously) commissioned Major General of Volunteers in March 1863 to date from 18 July 1862.
References & notes
Basic military history from Cullum's Register.1 His Cullum number is 287.
More on the Web
For more about the aftermath of General Mansfield's death, see an excellent post by John Banks, source also of Mansfield's picture, from a Brady photo at the Middlesex County (CT) Historical Society.
12/22/1803; New Haven, CT
9/18/1862 Sharpsburg, MD; burial in Indian Hill Cemetery, Middletown, CT