Jan III van Montfoort (or Johan van Montfoort), (c. 1448 – 28 March 1522) was Viscount of Montfoort, Free Lord of Zuid-Polsbroek, Free Lord of Purmerend-Purmerland, and a leader of the Hook Party in the Bishopric of Utrecht.

Jan van Montfoort opposed the Burgundian rule of the Utrecht in the person of Bishop David of Burgundy.

After the Siege of Utrecht (1483) peace was concluded but Jan van Montfoort lost his Fiefs of Purmerend-Purmerland and Zuid-Polsbroek, which were confiscated and given to nobles close to Maximilian of Austria.

Jan married on 16 December 1475 with Wilhelmina van Naaldwijk.

They had: Jan remarried on 12 June 1509 with Charlotte van Brederode, and had: