Riesi is a comune in the Province of Caltanissetta in the Italian region Sicily, located about 110 kilometres southeast of Palermo and about 20 kilometres south of Caltanissetta. As of 31 December 2004, it had a population of 11,678 and an area of 66.6 square kilometres. Riesi borders the following municipalities: Barrafranca, Butera, Mazzarino, Pietraperzia, Ravanusa, Sommatino.