William of Nassau (1487-1559), count of Nassau-Dillenburg, was a nobleman of the house of Nassau. He was the brother of count Henry III of Nassau-Breda and the father of William I of Orange. He was called William the Rich (Dutch: Willem de Rijke).

He was married to Walburga van Egmond (1489-1529) and later to Juliana of Stolberg (1506-1580).

His son William inherited the principality of Orange. The House of Orange-Nassau (and the Dutch royal family) descends from him.

Sons & daughter:

• William I of Orange
• Johan of Nassau
• Louis of Nassau
• Henry
• Mary