The patron saint of Montoggio is Saint John Beheaded (San Giovanni Decollato), celebrated on the second-to-last Sunday of August. The parish church named after him dates from the 12th century but was completely rebuilt towards the end of the 17th century: behind a modest façade it holds numerous 17th- and 18th-century works of art.
The town was a fief of the Malaspina family from 1164, by grant of Emperor Frederick Barbarossa, after having been a possession of the bishops of Tortona; its castle was the scene in 1547 of the Fieschi conspiracy against the Republic of Genoa, when the Genoese army, led by captain Agostino Spinola, besieged the stronghold occupied by Gerolamo Fieschi after the death of his brother Giovanni Luigi, and on the suggestion of admiral Andrea Doria had it mined and destroyed. Near the ruins, where Gerolamo Fieschi himself was beheaded, the townspeople had built a chapel in the 15th century holding a wooden effigy of the saint.
