William I, Count of Nassau-Dillenburg

William I, Count of Nassau-Dillenburg (1487-1559) was a count of the House of Nassau who held several counties including Nassau-Dillenburg, Nassau-Siegen, Nassau-Dietz, and Vianden. He was born in Dillenburg, Germany and held citizenship in both Germany and the Netherlands. He was the father of several notable figures including William the Silent, Louis of Nassau, and Johann VI, Count of Nassau-Dillenburg. He was the son of Elisabeth of Hesse-Marburg and Johann V of Nassau-Vianden-Dietz.

Throughout his time as a count, William I earned the nickname "the Rich". His official title was William I, Count of Nassau-Dillenburg, and he held occupations as a Count and Politician.

William I had various children, including Maria of Nassau (1539–1599), Anna of Nassau-Dillenburg (1541–1616), and several others, such as Anna, Elisabeth, Catherine, Juliane, Magdalena, Maria (1556–1616), Adolf, and Henry of Nassau-Dillenburg.

William I, Count of Nassau-Dillenburg, passed away in Dillenburg on October 6, 1559.