The patrons of Isola del Cantone are Saints Stephen and Innocent, celebrated on the second Sunday of August. The parish church of San Michele Arcangelo, in the main village, was founded by Benedictine monks between the 12th and 13th centuries and later attached to the Sacra di San Michele of the archdiocese of Turin; the current building dates from the 17th century, and the parish, unlike the others in the municipality, belongs to the archdiocese of Genoa.
The municipal territory holds three castles: the Spinola castle of Cantone, erected according to some accounts in the 14th century and today almost entirely absorbed into the adjacent buildings; the Spinola-Mignacco castle, built with a square plan by Captain Guglielmo II Spinola between 1553 and 1562 and still owned by the Mignacco family; and a further defensive structure from the 11th and 12th centuries in the hamlet of Montessoro, of which two towers remain partly visible. In 1235 the fief passed to the Malaspina family and from 1256 to the Spinola family, who held it until 1797 among the imperial fiefs of the upper Scrivia valley, abolished by Napoleon Bonaparte. The Spinola castle of Cantone today houses the archaeological museum of the upper Scrivia valley, opened in 2013, which holds finds from prehistory to the 20th century.
