John or Jan van Diest (died 1 June 1340) served as Bishop of Utrecht from 1322 until his death in 1340.
[1] Jan descended from a noble family from Brabant, and was initially provost of Cambrai.
The latter was confirmed by the archbishop of Cologne, but Pope John XXII intervened, declaring the choice of the Utrecht chapters void, and personally consecrated Jan van Diest in Avignon.
Upon taking office, Jan immediately inherited a large debt from his predecessors.
William III threatened to take over the Nedersticht, and it was only because of the resistance of its citizens that the independence of the bishopric was maintained.