William I, Count of Sancerre

William I (c. 1176–1217) succeeded his father Stephen I as Count of Sancerre in 1191, and in 1211 married Eustachie of Courtenay, sister of Peter of Courtenay. On 27 July 1214 he fought at the Battle of Bouvines in the army of Philip II, as lieutenant of his cousin Odo III of Burgundy.

In 1217 he accompanied his brother-in-law Peter II of Courtenay, newly elected Latin Emperor, toward Constantinople by land after the failed siege of Durazzo. In the Albanian mountains Theodore Komnenos Doukas of Epirus ambushed and captured them, and William died in Epirote captivity. His son Louis I succeeded him.