Nothing is known about this MP before his appointment to the Huntingdonshire bench in 1372, when he must still have been a comparatively young man. His subsequent activities as a farmer of pavage at Yaxley suggest that he spent part, if not all, of his early life there, and although he was later able to consolidate his estates through purchase, his connexion with this small Huntingdonshire village to the south of Peterborough remained strong until his death. It was, indeed, at Yaxley that he and his wife were permitted by the bishop of Lincoln, in 1398, to celebrate mass privately in their own chapel. By then Herlyngton had accumulated other holdings across the county border in both Northamptonshire and Cambridgeshire, where he enjoyed considerable influence among the local gentry. His major acquisitions of property were, however, confined to Huntingdonshire, and appear to have been made at two separate points in his career. Firstly, in 1381, he took on the lease of a substantial estate in Abbotsley and Upper Hardwick (near St. Neot’s) from Richard Knyvet, who fixed the rent at 40 marks a year, but subsequently agreed to sell him some of the property outright. Several years later, at the very end of the 14th century, Herlyngton bought the whole manor of Orton Waterville, together with the advowson of two chantries in the parish church, from the trustees of the Thorpe estates. He was, moreover, twice able to supplement his landed income by farming property from the Crown. In October 1380 he and Sir William Brantingham were given custody of certain confiscated land in the Huntingdonshire village of Folksworth; and towards the very end of his life he and another associate took over the lease of holdings in the same area during the minority of Humphrey, earl of Stafford.
Most of the information which now survives about Herlyngton concerns his involvement in the affairs of other landowners, and although nowhere specifically described as such, it seems likely that he was a lawyer. From 1373 onwards he witnessed a number of local deeds, most notably for the courtier, Sir William Thorpe (then owner of Orton Waterville), various members of the influential Styuecle family and their kinsman, Sir William Moigne, who was one of his neighbours.
Herlyngton was not slow to invoke the law on his own account, and he spent some time in court as a result of private quarrels rather than professional commitments. During the early 1380s, for example, he sued a priest named John Eysham for trespassing on his Northamptonshire estates, and not long afterwards he took another clergyman to court for the detinue of an unspecified book. His last years were marked by actions for debt brought against two local men who both managed to escape the full force of the law, although this round of litigation was somewhat overshadowed by a far more serious case which reached the court of Chancery in January 1405. Herlyngton was then bound over in securities of 1,000 marks to keep the peace towards one John Peeke, who offered similar guarantees that he would do no harm either to him or his servants.
