| Conventional Long Name: | Duchy of Montferrat |
| Common Name: | Montferrat |
| Era: | Modern Era |
| Status: | Duchy |
| Religion: | Catholicism |
| Leader1: | Guglielmo Gonzaga (first duke) |
| Leader2: | Ferdinando Carlo Gonzaga (last) |
| Year Leader1: | 1574–1587 |
| Year Leader2: | 1665–1708 |
| Title Leader: | Duke |
| Year Start: | 1574 |
| Year End: | 1708 |
| Event Start: | March of Montferrat raised to a duchy |
| Event1: | War of the Mantuan Succession |
| Date Event1: | 1628–31 |
| Event2: | Claims by House of Savoy confirmed |
| Date Event2: | 1648 |
| Event End: | Annexed by Duchy of Savoy |
| Event Post: | Treaty of Utrecht |
| Date Post: | 1713 |
| P1: | March of Montferrat |
| Flag P1: | Flag of Montferrat.svg |
| S1: | Duchy of Savoy |
| Flag S1: | Savoie flag.svg |
| Flag: | Flag of Piedmont#March of Montferrat |
| Flag Type: | Flag |
| Symbol: | Byzantine flags and insignia#Tetragrammatic cross |
| Capital: | Casale Monferrato |
| Currency: | Cavallotto, Ducat |
The Duchy of Montferrat was a state located in Northern Italy. It was created out of what was left of the medieval March of Montferrat after the last Palaeologus heir had died (1533) and the margraviate had been briefly controlled by the Emperor Charles V (until 1536). After that brief interlude, it passed by marriage of the last heiress, Margaret of Montferrat, to the House of Gonzaga, already dukes of Mantua. In 1574 the fief was elevated from Marquisat to Duchy.[1]
Its territory, located in southern Piedmont, is still known today as Montferrat.[2] [3]
At that time, the state of Montferrat had an area of 2750 km2, and consisted of two separate parts bordered by the Duchy of Savoy, the Duchy of Milan, and the Republic of Genoa. Its capital was Casale Monferrato.
With the War of the Mantuan Succession (1628 - 1631), a piece of the duchy passed to Savoy; the remainder passed to Savoy in 1708, as Leopold I, Holy Roman Emperor, gained possession of the principal Gonzaga territory, the Duchy of Mantua.