The beginnings of the County came in 1102, when Count Raymond IV of Toulouse, one of the leaders of the First Crusade, began a lengthy war with the Banu Ammar Emirs of Tripoli (theoretically vassals of the Fatimid caliphs in Cairo), gradually seizing much of their territory and besieging them within Tripoli itself. Raymond died in 1105, leaving his infant son Alfonso-Jordan as his heir, with a cousin, William-Jordan of Cerdagne, as regent. William-Jordan continued the siege of Tripoli for the next four years, when a bastard son of Raymond, Bertrand, who had been acting as regent of Toulouse, arrived in the east, leaving Toulouse to Alfonso-Jordan and his mother, who returned to France. Bertrand and William-Jordan, due to the mediation of King Baldwin I of Jerusalem, eventually came to an agreement whereby each would keep control of their own conquests, an agreement which Bertrand got the better part of when he captured Tripoli later that year. When William-Jordan died a few months later, Bertrand became sole ruler.
The County of Tripoli continued to exist as a vassal state of the Kingdom of Jerusalem, while within the county itself the Knights Hospitaller were given an autonomous castle in 1142, Krak des Chevaliers. Count Raymond III, who reigned in Tripoli from 1152 to 1187, was an important figure in the history of the Kingdom to the south, due to his close relationship to its Kings (his mother Hodierna was a daughter of Baldwin II of Jerusalem) and to his own position as Prince of Galilee through his wife. He acted twice as regent for the Kingdom, first for the young Baldwin IV from 1174 to 1177, and then again for Baldwin V from 1185 to 1186, and acted as the leader of the local nobility in their opposition to Baldwin IV's Courtenay relations, to the Templars, to Guy of Lusignan, and to Raynald of Chatillon. Raymond thus unsuccessfully argued in favor of peace with Saladin, but, ironically, it was Saladin's siege of Raymond's Countess in Tiberias that led the Crusader army into Galilee before its defeat at Hattin in 1187, and although Raymond survived the battle, he died soon afterwards.
The County managed to avoid being conquered by Saladin in his string of victories following Hattin, and Bohemund IV, second son of Bohemund III of Antioch, succeeded to it upon Raymond's death. After Bohemund III's death in 1201, the County was in personal union with Antioch for all but three years (1216-1219) until Antioch's own fall to the Mamelukes in 1268. Tripoli survived for a few more years.
The death of the unpopular Count Bohemund VII in 1287 led to a dispute between his heir, his sister Lucia, and the city's commune, which put itself under the protection of the Genoese. Eventually, Lucia came to an agreement with the Genoese and the Commune, which displeased the Venetians and the ambitious Bartholomew Embriaco, the Genoese mayor of the city, who called in the Mameluke Sultan Qalawun to their aid. Qalawun captured the city after a siege in 1289, bringing the history of the County to an end.
Counts of Tripoli, 1102-1289