Guillaume is shown as gardien des iles in letters of Henri III of 8 and 27 September and 14 October 1227.
He was appointed for a further term, in 1232, along with Philippe d'Aubigné, as Warden of Jersey, Guernsey and Sark, but in October that year he was recalled on another mission, leaving d'Aubigné in sole charge of the islands, now including Alderney.
William was born in Basing, Hampshire, the son of Adam de Port, Lord of Basing, and Mabel de Orval , Heiress of Halnaker and St Jean. Mabel's mother, Muriel de St Jean, inherited the family estates in Saint-Jean-le Thomas, near Avranches in Normandy and when they eventually passed to William, he adopted the name de St Jean, styling himself "Willelmus de Sancto Johanne secundus," when he later executed a charter for Boxgrove Priory "pro animabus Willelmi et Roberti de Sancto Johanne et Ade de Port patris mei et Mabilie matris mee".
The change of name is curious, since the family of Port, both in ancestry and landed estate, was more important than that of St John.
On the conquest of Normandy, William adhered to King John and his lands in Normandy were confiscated by Philip Augustus, King of France.
In 1203 he was shown on the Norman Exchequer Rolls as owing 12 livres 10 sous for scutage on the service of 21 knights, due on the fees of William d'Orval. Southampton Castle was committed to him on his father's death, and he was sheriff of Hampshire in 1214 and 1215. He was with John in his disastrous expedition in Poitou and Anjou in 1214. In February 1215 he was one of the King's emissaries to the Earls, Barons and people of Hampshire, and in November one of those charged to bring men from Angouleme, and stores from Corfe castle, to the King at Rochester; but later he joined the Dauphin, probably at the siege of Winchester, July 1216.
However, on 16 March 1217 he had a safe conduct to speak with the Earl Marshal, his lands having been granted on the previous day to John Marshal. In February 1220 he was "with the King" at the siege of Bytham; in February 1225 he witnessed the Forest Charter and the confirmation of Magna Carta. In 1230 he served in Henry's abortive expedition into France, and in 1233 was employed in defence of the South-east coast.
|Richard de Gray
1226-1227, 1229-1230, 1252-1254
|William de St Jean
|Henri de Trubleville