Most historians give a date of birth for John Guillim of 1565, in the county of Herefordshire. However, it is also recorded that he was the son of John Guillim of Westbury-on-Severn in Gloucestershire, and my searches of the parish records available at the Family Search site have discovered a John, born in about 1550 in the neighbouring village of Minsterworth, where he is said to have lived most of his life. This part of England is very close to the border with Wales and John's ancestors were almost certainly Welsh.
He was educated at Oxford University (possibly Brasenose College), but I have not been able to determine his subsequent profession. However, he might well have been back in Minsterworth by 1575 when a John Guillim married a local girl, Frances Dennis, and raised a family of one boy, John (1578), and three girls, Margaret (1580), Frances (1582) and Priscilla (1584).
The first record of his involvement with heraldry is the Earl Marshal's Warrant, dated 23 February 1604, permitting him to bear the tabard of the Portsmouth Pursuivant Extraordinary. Then, from Michaelmas 1613, he received a salary from the College of Arms as Rouge Croix Pursuivant.
John's death is recorded as having occurred on 7 May 1621, probably also at Minsterworth, although there is no record of his place of burial.
The Display of Heraldry was written in 1610, and my copy is from the reprinted first edition of 1611. There were seven further editions of the book following John's death, the last one (described as the "sixth") being in 1724. Some historians have suggested that the original author of the Display of Heraldry was a clergyman named John Barkham who was unwilling to have the work published in his own name (the subject matter seeming unfit for a clerical man !), but this claim is not widely supported today.
I am very grateful to John Neitz, who kindly supplied me with information for
these notes from works in his possession concerning the history of the College of Arms.
Mrs Elizabeth Boardman, the Brasenose College Archivist, was also very helpful with details from the Alumni
Oxoniensis 1500-1714 and the Dictionary of National Biography.