William I, Lord of Coucy

Guillaume I de Coucy (1288–1335) was a Picard baron, lord of Coucy and Oisy. The son of Enguerrand V de Coucy and Christine Lindsay, a niece of King John of Scotland, he married Isabelle de Châtillon in 1311.

He held Oisy through the marriage and succeeded his father at Coucy around 1323. Jeanne of Flanders, widow of Enguerrand IV, disputed both lands. His claim was upheld in April 1329, when Philip VI settled the long family suit in his favour. He died in 1335 and was buried at Prémontré Abbey.