O'Neill, John (1834–78), Fenian and US army officer, was born 9 March 1834 in Drumgallon, parish of Clontibret, Co. Monaghan, youngest of three children born to Elizabeth O'Neill. His father (name unknown) died five weeks before his birth. Raised by his paternal grandparents from the age of six, he remained in Monaghan for five years after his siblings joined their mother in Elizabeth, New Jersey, in 1843. Receiving a primary education at Clontibret national school, he emigrated to the USA in 1848. Between 1849 and 1857 he worked as a shop clerk and travelling salesman before setting up a catholic bookshop in Richmond, Virginia. Selling his store in the summer of 1857, he enlisted in the 2nd US Dragoons, hoping to see action in the Mormon rebellion in Utah that year. Feeling cheated out of combat when the rebellion collapsed, he deserted and re-enlisted in the 1st Cavalry, which was fighting minor wars with Native Americans in California. Having reached the rank of sergeant in peacetime, he was promoted to second lieutenant in the 5th Indiana Cavalry after taking part in the peninsular campaign of May–July 1862 during the American civil war. Promoted to first lieutenant in April 1863, he fought with distinction during a number of skirmishes incident to the Ohio raid of Gen. Morgan in June 1863. Chagrined not to get further advancement by early 1864, he resigned from the cavalry and was commissioned captain in the 17th US ‘coloured’ infantry regiment, retiring wounded in November that year.
In October 1865, while working as a government pension agent in Nashville, Tennessee, he joined the Fenian faction led by W. R. Roberts (qv), undertaking to organise the city. Attracted by the grandiose plans to invade Canada drafted by Gen. Thomas Sweeny (qv), he made himself available to lead a detachment of Fenian volunteers (mostly discharged army veterans) in one of the diversionary attacks due for the summer of 1866, hoping to exploit Anglo–American tensions and perhaps spark a war between Britain and America. Though originally assigned a secondary role in the invasion, O'Neill later claimed that the concept had been his own. On 28 May 1866 O'Neill took some 400 men disguised as railroad labourers by train to Cleveland, where they joined another 1,600 Fenian troops. When Brig.-gen. William F. Lynch, the expedition commander, fell ill, O'Neill was given charge of the troops and ordered to cross the Niagara river and form a bridgehead on the Canadian shore controlling the Welland canal.
At 3 a.m. on 1 June about 800 Fenians in motley uniform (blue-grey and green, some with buttons inscribed ‘IRA’ for ‘Irish Republican Army’, as the force was termed) were ferried across in barges. While one unit took possession of the ruined Fort Erie, the remainder marched into Erie village. As Canadian militia reserves encircled the rough headland, O'Neill doubled back unexpectedly, taking one section of the massing forces by surprise in an aggressive sortie. The manoeuvre resulted in a triumph for the Fenian troops at Ridgeway Hill on 2 June over the inexperienced Queen's Own Rifles (a student militia). However, after reinforcements failed to arrive, O'Neill decided to retreat. Following a skirmish at Port Colbourne, he evacuated 700 men to Buffalo. Casualties amounted to sixteen Canadians killed and seventy-four wounded, compared to eight Fenians killed and twenty wounded. Some 117 Fenians were, however, taken prisoner. After a short detention on charges of violating US neutrality laws, O'Neill and his subordinates were released.
Though it was clear that Washington would not countenance filibustering of this sort against British colonial territory, and that there were few enough Irish-American ex-soldiers prepared to become involved, O'Neill strove to mobilise another invasion force. Made inspector-general of the Irish republican army in September 1866, he was elected to the Fenian senate, and was known by the honorary title of ‘General’. In late 1867 he replaced Roberts as Fenian president, opening negotiations with the John O'Mahony (qv) branch of Fenianism for a united movement. By early 1868 his organisation had been penetrated by Canadian and British agents, who included Henri Le Caron (qv) (T. M. Beach), with whom O'Neill was close. By 1869 O'Neill was bitterly at odds with the majority of his senate, and was allegedly drinking and embezzling Fenian funds. On 25 May 1870 he led a confused raid over the Vermont border, and was arrested by a US marshal. Sentenced to two years’ imprisonment in July, he was pardoned in October 1870. He undertook a final, yet still more absurd, attempt on the Canadian frontier on 5 October 1871 in Minnesota, which was foiled by ignorance as to the location of the border with Manitoba. Between 1872 and 1876 he worked manfully to establish pioneer Irish settlements in Nebraska – ‘the next best thing to fighting for Ireland’ (Noonan, 284) – for humanitarian purposes and with the vague ambition of training Irish-American youth in warfare. His labours were crowned with the creation of the town of O'Neill, Nebraska. It was in such practical endeavours that the unworldly O'Neill most successfully overcame a tendency to mystical self-absorption. He died of pneumonia 8 January 1878 in St Joseph's hospital, Omaha, and was buried in Holy Sepulchre cemetery, Omaha.
He married (27 November 1864) May Crowe of San Francisco, allegedly a former Sister of Mercy who was nursing war wounded in Nashville. They had three children.