Sir William Hardy (1807–1887) was an English archivist and antiquarian.
In February 1823, he obtained an appointment at the Tower of London, under Samuel Lysons, similar to the one his brother had obtained in 1819: Lysons was their uncle. Seven years later he was offered and accepted the post of keeper of the records of the Duchy of Lancaster. In 1839 he was elected a fellow of the Society of Antiquaries. He had also a private practice in antiquarian, legal, and genealogical inquiries, and made a reputation: he was consulted in numerous disputes on foreshore fishery and common rights, and was well known for applications made to the House of Lords for the restoration of peerages in abeyance.
While at the Duchy of Lancaster he worked on arranging the muniments. In 1868 Queen Victoria decided to present the duchy records to the nation, and incorporate them with the public archives. Hardy was then transferred to the Public Record Office and appointed an assistant-keeper in there. In 1878, on the death of his brother, Sir George Jessel offered him the post of deputy-keeper, which he held for eight years. He resigned, in poor health, on 27 January 1886.
Results of his work appeared in the reports of the Public Record Office. Besides the calendars to the Duchy of Lancaster records, he compiled, in 1845, Charters of Duchy of Lancaster, with the major documents on the formation of the Duchy and historical introduction. During his time of office as deputy-keeper he drew up a scheme for reorganising the department, which was carried into effect. He was also instrumental in starting the Commission for the destruction of valueless documents.
In 1840 he married at Lewisham Church, Kent, Eliza Caroline Seymour Lee, daughter of Captain J. E. Lee, by whom he left two sons, the younger being William John Hardy, father of William Le Hardy, making three generations of archivists.
This article incorporates text from a publication now in the public domain: Hardy, William John (1890). "Hardy, William". In Stephen, Leslie; Lee, Sidney (eds.). Dictionary of National Biography. 24. London: Smith, Elder & Co.