Eustace III (c. 1050 - c. 1125) was the count of Boulogne from 1087 succeeding his father, Eustace II. He joined the First Crusade, being present at Nicaea, Dorylaeum, Antioch, and Jerusalem. After fighting in the battle of Ascalon, he returned home. Initially offered the Kingdom of Jerusalem, Eustace was at Apulia when he received news of Baldwin of Bourcq's election to the throne. On his return to Boulogne, he founded a Cluniac monastery in Rumilly, retired as a monk, and died in 1125.