No direct evidence has survived of Yerde’s early life or family, although his strong connexions with the south-west of England, where he almost certainly spent his youth, suggest that he was perhaps the son of the John Yerde who, in 1377, held the Devonshire manors of Yard and Burston as tenant of the earl of Devon. He may also have been related to Simon Yerde of Wye in Kent, a local commissioner during the 1380s, but this remains open to conjecture.
Yerde’s services were clearly felt to be worthy of reward. In March 1402, for example, he was made collector of customs at the port of London, and in November 1403 he and Thomas Prudence shared a gift of 20 marks in recognition of their diligence in preventing frauds and concealments by foreigners in England. When he was not engaged in royal business, Yerde seems to have spent this part of his life in the south-west. Stephen Trenewith, a Cornish lawyer, offered him recognizances of £22 10s. in July 1402; and it was as William Yerde of Somerset that he went surety for Sir John Cornwall (later Lord Fanhope) when, in October 1405, the latter became farmer of some of the late earl of Huntingdon’s estates. Yerde and Sir John were then also acting as joint feoffees-to-uses of certain property in Hertfordshire, having no doubt become friends as a result of Sir John’s marriage to Huntingdon’s widow, Elizabeth of Lancaster, sister of Henry IV, who may well have had a hand in the rehabilitation process. At about this time Yerde began a lawsuit in Chancery over the exercise of certain feudal and judicial rights in Nansloe, Polgrain and part of the manor of Coddiford Farleigh, where he may have been given land by Lord Botreaux. We do not know exactly when Yerde acquired property in Surrey, although he had probably settled there before being made sheriff in 1408. At the time of his first return to Parliament in March 1413, he owned land worth £20 p.a. in the county and also had a term as escheator of Surrey and Sussex to his credit. Perhaps his successful career at Court led him to purchase estates nearer London, where he must have spent a considerable amount of time, especially after being promoted to the rank of harbinger of the royal household in 1411. Towards the end of his life Yerde held other property in Hinxworth (Hertfordshire), Meddon (Devon) and ‘Wyke’ (Cornwall), but, again, its provenance is not recorded.
One of the most striking features of Yerde’s career is his longstanding association with the Holand family, which he loyally maintained despite his experiences at the beginning of the century. In April 1416 he undertook to act as an attorney at the Exchequer for John Holand, the late earl of Huntingdon’s second son and heir, during his absence in France (at Harfleur). Holand was formally restored to his father’s estates and earldom in 1417, and from then onwards Yerde played an important part in his affairs. In July 1420 the MP offered sureties of £1,000 in Chancery as an earnest of his readiness to account before a specially appointed body of auditors for any money received by him in the earl’s name either before or during the next two months; and in the following February (1421) he was chosen to desputize for Huntingdon in his capacity as constable of the Tower of London. Yerde’s appointment terminated abruptly on the escape from his custody of five distinguished prisoners (including the traitor, Sir John Mortimer, a lollard named Thomas Payn and two prisoners of war), whom it was alleged he had assisted in their flight. On 27 May 1422, Sir John Cornwall and others stood bail of £100 (to which Yerde himself added a further £500) for his appearance before the royal council; and in February 1423 Yerde offered the earl of Huntingdon recognizances of £2,929 7s.9d. on the security of his Surrey estates as a guarantee that he would answer any charges of negligence or worse put to him in Chancery. Huntingdon had by this date already spent two years as a prisoner of war in France, so it was with the dual purpose of securing a pardon for himself and helping to obtain his patron’s release that Yerde took his seat in the Commons of 1423. His first aim proved completely successful; and on 20 Oct., the day on which Parliament met, letters patent were issued restoring his confiscated property and freeing him from any blame over the incident.
Very little is known about Yerde’s other affairs, although it seems that his relationship with the Botreaux family remained fairly close. At all events, William, the 3rd Lord, continued to pay his annuity, which was increased to £6 13s.4d. at some point before 1421, when he and his wife, Alice, shared the grant jointly for life. His dealings with other members of the Botreaux affinity were not always cordial, however, and he may already have begun suing one of Lord William’s esquires for a debt of £42 13s.4d. In February 1424 a recognizance for 100 marks (later cancelled) was offered to him by Botreaux’s younger brother, Sir Ralph Botreaux, perhaps as a result of this dispute.