San Giulio Island (Isola di San Giulio) is an island within Lake Orta in Piedmont, northwestern Italy. The island is 275 meters long (north/south), and is 140 meters wide (east/west). The largest structure on the island is the Basilica of Saint Giulio. The island, just west of the lakeshore village of Orta San Giulio, has some very picturesque buildings, and takes its name from a local saint (Julius of Novara), who lived in the fourth century.
In the 9th century the bishop of Novara built the Basilica of Saint Giulio on the island.
William of Volpiano (Saint William of Dijon) was born here in 962, in the family citadel located on the island.