Following the collapse of the Western Roman Empire, Germanic Lombards occupied the area, before they in turn were conquered by the Normans.

When Sicily seceded in the Vespers of 1282, the mainland possessions of the Normans, including San Massimo, became the Kingdom of Naples.

The first reference to San Massimo, dating to 1113 CE, occurs in the locative surname of a Norman nobleman, De Sancto Maximo.

[6] The Church of Santa Maria delle Fratte was erected in the 12th century, and rebuilt on several occasions after devastating earthquakes that nearly leveled San Massimo in 1456 and 1805.

The municipality of San Massimo contains the frazione (subdivision) Campitello Matese, located at 1,450 metres (4,760 ft) above sea level, which shares its name with its ski resort, one of the foremost in Central and Southern Italy.