Casoli is a comune and town in the Province of Chieti in the Abruzzo region of Italy: it is situated on a foothill of the Majella mountain, at the base of which runs the Aventino River, tributary of the Sangro. As of 31 December 2004, it had a population of 5,901 and an area of 66 square kilometres (25 sq mi).Casoli borders the following municipalities: Altino, Civitella Messer Raimondo, Gessopalena, Guardiagrele, Palombaro, Roccascalegna, Sant'Eusanio del Sangro.