Willoughby, Charles (c.1630–1694), physician, was born in Co. Cork, son of Sir Francis Willoughby, a major-general in the army of Charles I and member of the provincial council of Munster, who was appointed governor of Galway in 1636. Charles Willoughby seems to have studied at TCD (though he is not recorded as doing so in Alumni Dublinenses – the sources are thin for this period): on taking the degree of BA at Oxford in 1649 he is described as 'of Trinity College Dublin'. In the same year he was elected fellow of Merton College and proceeded MA in 1652. He enrolled at Padua University to study medicine on 5 November 1662 and graduated MD in March 1663/4. He was incorporated MD at Oxford in 1664. In 1663, having presumably returned from Italy, he presented a collection of botanical specimens made there to Merton.
By 1667 he had moved to Dublin, for he was nominated a fellow of the Irish College of Physicians in its charter of that year; he was elected president in 1676, and served as treasurer (1677–83). On 25 July 1683 he was elected a fellow of the Royal Society of London. He seems to have had a flourishing practice in Dublin (based more on herbal than on chemical remedies) and to have attended persons prominent in church and state. Not that this prevented him from seeking other pastures, as when he wrote in 1682 to the lord lieutenant, the duke of Ormond (qv), to point out that his 'liberall and universall' education fitted him for a 'superior sphere than the managery of a glyster-pipe; a trade of so much slavery that I never intended to follow otherwise than for want of better employment' (HMC, Ormonde manuscripts, i (1895), 104).
Willoughby was an active member of the Dublin Philosophical Society, which had been founded in October 1683, largely by William Molyneux (qv). He acted as the society's first director and then as its president. He contributed actively to meetings, talking about meteors in Italy, optics, and the lines of latitude and longitude. He also read two papers (now lost) on hermaphrodites and on 'A remarkable case in physic'. He was one of a committee of four which drew up the society's rules in January 1684 and was again active when the society was revived after the Williamite settlement in 1693.
In 1691 he wrote a paper on the Dublin bills of mortality (and on quinine) in response to a query from John Locke. A copy of this (dated 17 April) survives in Bodl. Rawlinson MS C.406 and is printed in K. Dewhurst, 'The genesis of state medicine in Ireland', Irish Journal of Medical Science, 6th series, no. 368 (1956), 370–83 (where are also printed two letters from Patrick Dun (qv) to Locke on medical matters). A version (not known to Dewhurst) from a manuscript once held at TCD (now seemingly lost) is printed in RIA Proc., vi (1856), 399–416, where it is dated 1690.
Willoughby was continued a fellow of the Irish College of Physicians in its second charter of 1692 and acted as censor from then until his death. He died some time between 28 August (when he signed his will) and 1 September 1694 (when it was ordered 'that as a mark of our respect to our honoured colleague Dr Willoughby every one of the fellows in town doe appear att his funeral tomorrow in a gown under the penalty of a crown for the use of the College'). The MS catalogue of Willoughby's personal library – an interesting collection – survives as TCD, MS 10 (formerly MS E.4.9).