John of Ibelin (1215 – December 1266), count of Jaffa and Ascalon, was a noted jurist and the author of the longest legal treatise from the Kingdom of Jerusalem. He was the son of Philip of Ibelin, bailli of the Kingdom of Cyprus, and Alice of Montbéliard, and was the nephew of John of Ibelin, the "Old Lord of Beirut". To distinguish him from his uncle and other members of the Ibelin family named John, he is sometimes called John of Jaffa.
His family was the first branch of Ibelins to have their seat in Cyprus, due to his father's regency there 1218-1227. In 1229 John fled Cyprus with his family when Frederick II, Holy Roman Emperor seized the Ibelin territories on the island. They settled temporarily in northern Palestine, where the family had holdings. He was present at the Battle of Casal Imbert in 1232, when his uncle John of Beirut defeated Riccardo Filangieri, Frederick's lieutenant in the east. Around 1240 he married Maria of Barbaron (d. 1263), the sister of Hethum I of Armenia and sister-in-law of King Henry I of Cyprus. In 1241 he was probably responsible for drafting a compromise between the Ibelins and the emperor, in which Simon de Montfort, 6th Earl of Leicester would govern the kingdom. This proposal was never implemented and Simon never came to the Holy Land; the Ibelins continued to quarrel with the representatives of the Hohenstaufens, and in 1242 they captured Tyre from their rivals. John participated in the siege.
Shortly thereafter, sometime between 1246 and the beginning of the Seventh Crusade, John became count of Jaffa and Ascalon and lord of Ramla. Ramla was an old holding of the Ibelins, but Jaffa and Ascalon had belonged to others, most recently to the murdered Walter IV of Brienne, whose son John, Count of Brienne (king Henry's nephew) was supplanted by this Ibelin acquisition. This probably occurred when king Henry, John's first cousin, became regent of Jerusalem, and distributed continental lands to his Cypriot barons to create a loyal base there. Jaffa was by now a minor port and Ascalon was captured from the Knights Hospitaller by the Mamluks in 1247.