Count Jan IV of Nassau was Count of Nassau, Dietz and Dillenburg. He was the son of Engelbert I of Nassau, Count of Nassau and Dillenburg, Lord of Breda and Johanna van Polanen.
He married Maria of Loon-Heinsberg, Lady of Millen, Gangelt and Vucht, the daughter of John II of Loon, Lord of Jülich, Heinsberg and Löwenberg, on 7 February 1440. They had children, including:
Anna of Nassau
Johanna of Nassau
Ottillie of Nassau
Adriana of Nassau
Engelbert II of Nassau
Johann V of Nassau