Sources

1) Source: The Ecclesiastical History of England and Normandy: Volume III “The Countess Adela contributed large sums for the pope's expenses… William, the eldest, married the daughter of Gilo de Sulli… and left a worthy offspring, Odo, Rahier… Theobald, count Palatine… married Matilda, daughter of Duke Ingelbert… As for Stephen, the third son of Stephen de Blois, having been knighted by his uncle Henry, and taken prisoner William count of Mortain at the battle of Tinchebrai, the king granted him that county. He married Matilda, daughter of Eustace count of Boulogne, by his wife Mary ; and in her right inherited all his states” (Data from secondary evidence)
2) Source: Genealogia comitum Bulonensium A short genealogy connecting the early Merovingians to the later counts of Boulogne, written circa the 11th century. The earliest generations are almost certainly fictional. Considered a reliable secondary source for generations from Arnulf of Metz onwards. Considered a "primary" source for events from the year 1000 onwards.. External Link
https://www.dmgh.de/mgh_ss_9/index.htm#page/300/ (Data from direct source)
3) Source: The Ecclesiastical History of England and Normandy: Volume III "At the same time, Stephen, count de Blois, son of Theobald, count de Chartres, who was son-in-law of "William, king of England, took the cross and departed for Jerusalem"
4) Source: Chronica Magistri Rogeri de Houdene "He [Henry I] was succeeded by Stephen, his nephew, who reigned nineteen years" (Data from secondary evidence)