Conyngham, William Burton (1733–96), politician, antiquarian, and landowner, was second of two sons of Francis Burton , politician, of Buncraggy, Co. Clare, and Mary Burton, only daughter of Maj.-gen. Henry Conyngham, and sister of Henry Conyngham (qv), 1st Earl Conyngham. Little is known about his early life, though he is known to have been a student at Queens' College, Cambridge, from 1750, and in Lincoln's Inn from 1753. Pursuing a military career, he was commissioned (1759) captain in the army, and by 1766 had become lieutenant-colonel in the 12th regiment of dragoons. An energetic and innovative commander, in 1767 he re-structured the regiment as a light cavalry unit. He was MP for Limavady, Co. Londonderry (1761–76), Ennis, Co. Clare (1776–83, 1790–96), and Killybegs, Co. Donegal (1783–90), all constituencies associated with his family. He rarely opposed the government unless so instructed by his uncle, Henry Conyngham. Well regarded by contemporaries, he compiled a report to parliament on Ireland's fisheries which formed the basis of Arthur Young's (qv) work on the subject in 1780 and he was instrumental in the reform of fisheries legislation in 1781 and 1785.
He resigned his army commission in 1774 and was appointed commissioner and comptroller of the barrack board, an office worth £600 a year. The following year he was serving as aide-de-camp to the lord lieutenant, Earl Harcourt (qv), who rewarded him with the office of teller of the exchange, worth £1,500 a year. In 1777 he was made a privy councillor. He generally lived at Slane, Co. Meath, where he took charge of his uncle's estates. In 1763, in partnership with Blayney Townley Balfour of Townley Hall, and a Drogheda miller called David Jebb, Burton leased land and an existing mill building on the river Boyne from his uncle, and built there the largest flour mill in Britain or Ireland. It was for a generation or more the largest industrial building in Ireland; notable for its unusually elegant design and ornamentation, and was regarded as one of the most impressive structures of the day. The partners ploughed the considerable profits from the mill back into the business, and cleared all debts; they had received a loan from parliament to help offset its total cost of over £19,000. Burton was also involved with financing the Boyne Navigation canal, important for the success of his milling business, and with a cotton factory in Slane.
When Earl Conyngham died without issue in 1781, his estates were divided between his two nephews. Francis Pierpoint Burton inherited the estates in Co. Clare, Co. Limerick, and England, and the title ‘Baron Conyngham’. William inherited a life-interest in the estates in Co. Donegal and Slane, Co. Meath. On 3 May 1781 both brothers assumed by royal licence the surname Conyngham, and from that date William no longer used his original patronymic of Burton. Once he had full control of the estate at Slane, he employed the leading English architect James Wyatt (1746–1813) to renovate Slane Castle in the fashionable Gothic style, which accorded with Conyngham's lifelong interest in antiquities.
He was elected a member of the Dublin Society in 1758, and from 1772, he was involved with its antiquities committee, the first official body to take an interest in Ireland's archaeology. He was also associated with the direction of the Society's Drawing Schools. An important patron of artists such as John James Barralet (qv) and James Cavanah Murphy (qv), he employed the latter to survey and record the Moorish Gothic architecture of Batalha in Portugal and paid over £1,000 to bring out a volume of Murphy's drawings of the monastery and environs. From about 1765 he was appointed a trustee by parliament for the proposed academy of the Society of Artists in Dublin. In 1779 he personally commissioned the artist Gabriel Beranger (qv) to provide drawings of the ancient buildings at Glendalough, Co. Wicklow. He was also responsible for engaging Beranger on behalf of the Hibernian Antiquarian Society to do similar work in Connacht and other parts of Ireland. Burton had founded this society in 1779, and was its president. As William Conygham, he was one of the thirty-eight founding members of the RIA in 1785, was elected treasurer in 1785 (retaining this post until his death) and made a vice-president in 1792, but was occasionally dropped from the council for missing meetings. On his death he was found to owe the Academy the sum of £978. 4s. 8d., plus a quarter's interest at 4 per cent, which he had been holding for the Academy in his bank account. A committee cleared him of any wrongdoing, and the money was recovered from his estate.
He was recognized as the most munificent Irish patron of antiquarian research of his time, and the volumes of Grose's Antiquities of Ireland, completed by Edward Ledwich (qv) were dedicated to him in recognition of his efforts to publish a record of Ireland's architecture. His collection of antiquarian drawings and descriptions of ancient buildings, providing information about their appearance in the late eighteenth century, has been of considerable importance to later historians, though like his very fine library of antiquarian and other books, maps and manuscripts, it was dispersed after his death by his heirs, and the originals of some drawings have been lost. An ancient Irish harp, associated by later writers with Brian Bórama (qv) was presented by Conyngham to TCD, where it is one of the treasures of the college library.
Conyngham is also associated with pioneering investigations of Roman archaeological sites in Spain, in 1784 at the circus at Tarragona and also at the theatre at Sagunto; the latter was described in a paper to the RIA in 1789. Conyngham's role in excavating the Tarragona site was only confirmed in the 1990s; the name changes in the family, apparently compounded by mistakes made concerning the date of the excavation, led earlier authorities to ascribe the work to his uncle Henry Conyngham. During his travels in Spain and Portugal, he took an interest in contemporary developments that could be of benefit to Ireland, and sent home trade samples, seeds, and publications on trade, agriculture, and history. He shipped – at considerable expense – two Spanish rams back to Slane, for use in a breeding programme which he hoped would improve the quality of wool in Ireland. He also provided John Foster (qv), later speaker of the Irish commons, with much information about Portuguese trade.
His work with the RDS focused on the promotion of fisheries in the north-west of the country, and he was also interested in the production of salt, which was needed to preserve fish. An island off the north-west coast of Donegal, and part of Conyngham's estate, could hardly have been more remote from the markets of Dublin, but it was well known that huge herring shoals annually approached the coast. Conyngham had originally developed the mainland fishing village of Burtonport, named in his honour, but he decided that the offshore island, Rutland Island, which had a deep water harbour, was a still better prospect for investment, and from the late 1780s he planned and partly built a whole new town on the island, which he astutely renamed after the then lord lieutenant, the duke of Rutland (qv). His new town had warehouses, quays, streets of well-built houses, rope and salt works, and a massively redeveloped harbour and dockyard. As part of his efforts on behalf of the fishery, Conyngham built a new road from Mount Charles to Burtonport, through boggy and mountainous terrain. Experts and local gentry had claimed it would be impossible, so his success added greatly to his renown as an engineer. He spent £20,000 of his own money on the project, and petitioned parliament to match fund his enterprise; the Donegal Fishery Act of 1785 granted him this aid, and he may have spent at least another £10,000 to establish the town. The huge sums spent were at first justified by two successful herring fishing seasons, when thousands of workers brought back huge catches on over 330 boats; however, the combination of storms, which buried the new town under blown sand, and a collapse in fishing stocks, ended the Rutland Island enterprise after only a few years.
Conyngham's influence on town-planning elsewhere was more lasting. In 1772 he was appointed to the Dublin Wide Streets Commissioners, and for twenty-four years was one of the most active members of a very active body. He was involved with the widening of Dame Street, and with the aesthetically very successful extension of Sackville Street (latterly O'Connell Street) to a new bridge and thence to the front of TCD. He took a particular interest in the new road laid out between Park Gate and Islandbridge at the Phoenix Park, paying himself for the widening of about 800 metres of this impressive roadway which now bears his name. He held many other public appointments, and was made a lord of the Treasury in 1793. He was a governor of several charities and a fellow of the Society of Antiquaries of London.
A headstrong character, Conyngham was known for his volatile temper, which led him into many disagreements, and he fought several duels. He died 31 May 1796 at his town house in Harcourt Place, Dublin. He never married and his nephew Henry Conyngham (1766–1832), 1st Marquess Conyngham, inherited his Irish estates, thus re-uniting the Conyngham title and estates; Henry's twin, Sir Francis Nathaniel Burton (1766–1832), inherited the estates in Wales and a share in the Slane mill.