John Ernest of Nassau-Siegen (1582–1617)

John Ernest of Nassau-Siegen (Johann Ernst von Nassau-Siegen) was a German nobleman of the House of Nassau-Siegen. He was the second son of John VII, Count of Nassau-Siegen and Countess Magdalene of Waldeck-Wildungen.

Born on October 21, 1582, in Siegen, he served as a soldier in the Dutch States Army, participating in the Eighty Years' War against Spain. He distinguished himself in several military engagements.

John Ernest died unmarried and without issue on September 17, 1617, in Hulst, then part of the Dutch Republic. His death preceded that of his father, John VII, in 1623. The inheritance of the Nassau-Siegen territory was complex due to John VII's attempts to divide the county between his sons from his first and second marriages, a matter that led to considerable familial and political conflict after his death.