Willem van Nassau, Lord of De Lek (also Willem van Nassau-LaLecq, or in French Willem LaLecq; 18 August 1601 – 18 August 1627) was a Dutch soldier from 1620 until 1627. He was the illegitimate son of stadholder Maurice of Nassau, Prince of Orange and his mistress Margaretha van Mechelen.Like their other illegitimate children, he was recognized with the surname . He went by the title Rijksgraaf (Count of the Holy Roman Empire) van Nassau-LaLecq" and was also popularly known in French as the "Chevalier de Nassau". After 1625 he was granted lands and the title Lord of De Lek. He received his heerlijkheid of De Lek as a bequest from his father to him and his descendants. His brother Lodewijk van Nassau had the title "Lord of Beverweerd and Odijk".