Born: "At Sea", c.1831-4.
"Mr. James Salamander Devlin...was born at sea...aboard the gun-boat 'Salamander' and, according to the usual custom of those born at sea, was named after the ship." 
His enlistment and discharge details suggest he was born in 1831 or 1832, but his marriage certificate and obituaries imply 1834. If the latter, he would have been only 15 or 16 at enlistment. ]
[PB, Dec 2014: According to Wikipedia, the HMS Salamander was a steam vessel, one of the first true paddle warships, originally with a schooner rig but modified later. It was built in Sheerness and launched 14 May 1832. Its complement was 135. It would be good to know how and why James Devlin's parents were on board, since in its early years it appears to have been confined to the Channel. It was broken up in 1883.]
Enlisted: Athlone, Co. Westmeath, on the 8th of February 1850.
Age: 18 years 3 months.
Height: 5' 7".
Trade: None given.
Features: None given.
From Private to Corporal: 26th of March 1853.
Severely wounded in action at Balaclava.
Sent to Scutari on the 26th of October 1854 and invalided to England 21st of January 1854.
He was among the wounded soldiers seen by Queen Victoria on her first visit to Brompton Barracks, Chatham, on the 3rd of March 1855.
Sent from the Chatham Invalid Depot to Athlone, Ireland, "on sick leave till discharge", on the 30th of June 1855.
Discharged from Chatham Invalid Depot on the 6th of November 1855:
"Unfit for further service - Disabled after loss of power of left arm from a gun-shot wound and lance wound of the left shoulder."
Served 5 years 227 days. Aged 23 years 11 months on discharge.
Conduct and character: "a very good soldier." In possession of one Good Conduct badge.
Awarded a pension of 1/- per day. Living in Dublin in 1863.
A War Office letter, dated 5th of November 1891, had then recommended a "Special increase of 8d. per day for his services as a Pension Clerk from the 12th of September 1855 to the 1st of August 1872," but this was made up to 1/-, thus making his pension 24d. per day.
In April 1882 his pension was being sent to him c/o Sir John Rogerson Quay, situated in Dublin. (This is named after the property developer Sir John Rogerson who built the quay wall, reclaiming the former mud flats behind it. Rogerson was Lord Mayor in 1693-4 and commenced work on the wall in 1716 to protect them from flooding.)
Entitled to the Crimean medal with clasps for Alma, Balaclava,and Sebastopol, and the Turkish medal.
Awarded the Distinguished Conduct Medal, with a gratuity of £10, having been recommended for it on the 5th of February 1855. 
Attended the first Balaclava Banquet in 1875.
Member of the Balaclava Commemoration Society in 1877 and 1879.
Signed the Loyal Address to the Queen in 1887.
[RM/PB: In May 2006, a descendant, Mr Colin Langham-Fitt, provided the following information:
"James Devlin married Jane Partridge at Reepham with Kerdiston, in Norfolk on 22nd Jan 1857, age given as 23 (therefore date of birth 1834). Father's name shown as Denis Devlin (clerk). Family story has it he was the Governor of Athlone Gaol but I have been unable to prove or disprove this."
PB: Her father's name is given as "John Partridge". In 2014, Ancestry.co.uk did not have an image of the original document, whose reference was "England, Select Marriages, 1538-1973, FHL Film Number: 1596458 Reference ID: Item 25-29 p 45".
James Devlin to Jane Partridge, March Quarter 1857, Aylesham.
Holt Road, Wolterton, South Erpingham.
John Partridge, 60, Farmer.
Elizabeth Partridge, 45.
Jane Partridge [future wife], 7.
Three servants are also shown.
Pastures [poor writing] Farm, Dilham, Norfolk.
John Partridge, 72, wid[ower], Farmer 230 acres, 8 labourers, born Wickmere.
Thomas Partridge, 20, born Wolterton, Eliza Partridge, 23, born nr. Walsham.
Jane Partridge [future wife], 18, born Wolterton.
[This Jane Partridge makes sense - father's name, her age, and that part of Norfolk [CP]]
His gravestone (see below) refers to three children who pre-deceased him. But there may have been other children.
Charles Joseph, born c.1856, died 7th of April 1876, aged 20 years.
James Partridge, born c.1862, who died 5th of July 1883, aged 21 years.
Mary Ellen, born c.1883, who died 10th of October 1884, aged 1 year.]
There are references in an obituary (below) to another son, William Francis Devlin, and to a brother-in-law, Joseph H. Sheeran, hence to a surviving daughter referred to only as "Mrs Sheeran"."
According to obituaries, he was for several years the Chief Clerk in the Adjutant-General's Department, Dublin Castle.
James Devlin died 3rd of February 1892. He was buried in Grave No. AC75 (South), Glasnevin cemetery, on the 6th of February 1892. A head-stone was erected over the grave.
From the Irish Times, 5th of February 1892:
"Devlin - February 3rd., at his residence, 8 Connaught Terrace, Garville Road, Rathgar, James Devlin, Esq., late Chief Clerk, Adjutant-General's Department, Dublin Castle, aged 58 years. Funeral will leave at 10 o'clock tomorrow (Saturday) morning for Glasnevin Cemetery, R.I.P.
"We deeply regret to see announced in our obituary columns the death of Mr. James Devlin, late of the Adjutant-General's Department at Dublin. He was one of the survivors of the memorable charge of the Light Brigade at Balaclava, in which he was severely wounded and for which he was awarded, in addition to the Crimean medal with three clasps, and the Turkish medal, the "Medal for Distinguished Conduct in the Field." He was a general favourite, and will be deeply missed."
From the Broad Arrow,e 13th February 1892:
"4th Hussars - We regret to announce the death on the 3rd. inst. at Dublin, of Mr. James Salamander Devlin, late of this regiment.
He was born at sea, some 58 years ago, aboard the gun-boat "Salamander" and according to the usual custom of those born at sea, was named after the ship.
At the age of 19 he joined the 4th Light Dragoons and rode in the charge at Balaclava. This was his only action, for his sword hand was nearly severed with a sabre cut and he also received a bullet in the left shoulder. The bullet was extracted, and when, a few years ago, inflammation set in, the wound re-opened and did not close until a piece of his jacket came out, having been there for twenty-nine years. He was awarded the Crimean medal with three clasps, the Turkish medal and the medal for distinguished conduct in the field.
He had occupied for several years past the position of Chief Clerk in the Adjutant-General's Department in Dublin, and was a general favourite in the office, as indeed, with all who knew him.
The funeral took place on Saturday, the band and a firing-party of the 3rd Hussars being present on behalf of the 4th Hussars, now stationed at Colchester. Amongst the many tributes of affection and sympathy may be mentioned a beautiful wreath sent by the officers of the 4th Hussars."
From the Irish Times, 8th of February 1892:
"One of the Six Hundred." - On Saturday last the remains of Mr. James Devlin were laid in their last resting place in Glasnevin Cemetery. The sad ceremony was made more impressive by the presence of the band of the 3rd King's Own Hussars, on behalf of the 4th Queen's Own Hussars (late Light Dragoons) the deceased's old regiment, who now stationed at Colchester.
Amongst the many tributes of affection and sympathy may be mentioned a beautiful wreath sent by the officers of the 4th, as well as those sent by Mrs. Sheeran, Major Gorman, Major Grace, and Miss Cort.
The coffin, which was of solid oak, bore on its breast-plate the following inscription: 'James Devlin. Died 3rd February 1892. Aged 58 years. R.I.P.' The chief mourners were William Francis Devlin (son) Joseph H. Sheeran (brother-in-law) and James W. Dawson (nephew)... [A list of other mourners follows, mainly from the various Government Departments.]
After the recital of prayers by the Revd. J. Coffey, and J. Duane, Q.G.C., the usual volleys were fired, and thus honour was fully accorded to as gallant a soldier as ever drew sabre for his Queen and country."
From The History of the Dublin Catholic Cemeteries, William Fitzpatrick, 1900:
"A group of veterans, some of whom bore scars, attended in February of 1892 the burial of James Devlin, late of the Adjutant General's Office, one of the survivors of the 'Six Hundred' in the Cavalry Charge at Balaclava. That he should have escaped what Tennyson called the 'The mouth of Hell', and nearly 40 years after found a grave in the peaceful seclusion of Glasnevin Cemetery, was a blessing which his family gratefully recognised" (p194).
[PB: Available online in various formats at https://archive.org/details/historyofthedubl00fitzuoft (accessed 11.5.2014).]
His gravestone in Glasnevin Cemetery bears the inscriptions:
"In loving memory of Charles Joseph, eldest son of James Devlin, Adjutant-General's Office, Dublin, who died 7th of April 1876, aged 20 years.
"James Partridge, 2nd son, who died 5th of July 1883, aged 21 years.
"Mary Ellen, his child, who died 10th of October 1884, aged 1 year.
"Also of James Devlin, who died 3rd of February 1892, aged 58 years. 'One of the Noble Six Hundred.' Served with the 4th Queen's Own Light Dragoons in the Crimea and was severely wounded in the ever memorable Charge of the Light Brigade, 25th of October 1854."
At the base of the stone is "Rest, Warrior, rest, heed not the route. Until the trumpet sounds the grand 'Turn Out.' R.I.P."
At least 2 portraits. James Devlin also appears in a group photograph of survivors of the Light Brigade taken on 25th October 1887. He is in the back row, second from the right. [National Army Museum, accession no. NAM 1987-10-56.]. [Add info...]
Additional Census information for 1841 & 1851, and marriage registration, kindly provided by Chris Poole.
Wendy Leahy refers to his father as the governor of Athlone Gaol, citing an article on JD in The War Correspondent Vol. 28, No. 4, Jan 2011. Check this article. She also mentions his pension districts: 1855: Dublin 1, 1862: Carlow, Dublin 1, 1863: Carlow, Dublin 1, 1865: Dublin 1.