John of Isenburg-Grenzau (German: Jan von Isenburg-Grenzau) was the Count of Isenburg-Grenzau from 1554 until 1556, and the Archbishop of Trier from 1547 until 1556. John was the second son of Count Henry the Elder. His father only had the money to educate John and his brother Salentin, and they were both sent into the church. In 1547 he was elected the Archbishop of Trier. As archbishop, John reorganised the finances of the archdiocese, and worked to improve the standards of his father's lands. In 1554 John succeeded his brother Anthony as Count of Isenburg-Grenzau. John spent much time in his Westerwald residence of Montabaur, in which he died in 1556.