John I, Count of Nassau Dillenburg

John I, Count of Nassau-Dillenburg (German: Johann I. von Nassau-Dillenburg, Dutch: Jan I van Nassau-Dillenburg; c. 1340 – 4 September 1416, Keppel) was a Count of Nassau in Siegen and Dillenburg, both now in Germany. He was a son of Count Otto II of Nassau and Aleyda, Countess of Vianden.

John of Nassau married Margareta of the Marck on 30 November 1357. She was the daughter of Adolph II of the Marck and Margareta of Cleves. The dowry for this marriage was paid by Margareta's brother Engelbert of the Marck according to a charter from 1369. Their children include:

After the death of Count John I in 1416 his lands were not divided, but instead overseen by all four of his surviving sons Adolf, John II, Engelbert I and John III.