William I, Count of Boulogne

{{Short description|Count of Boulogne from 1153 to 1159}}

{{Use dmy dates|date=August 2019}}

{{Infobox royalty

| name = William I

| succession = Count of Boulogne and Earl of Surrey

| reign = 17 August 1153 – 11 October 1159

| predecessor = Eustace IV

| successor = Marie I

| spouse = Isabel de Warenne, 4th Countess of Surrey

| house = Blois

| father = Stephen, King of England

| mother = Matilda I, Countess of Boulogne

| birth_date = {{c.}} 1137

| death_date = 11 October 1159 (aged ~22)

| death_place = Toulouse, France

| place of burial = Hospital of Montmorillon, Poitou|

}}

William I ({{c.}} 1137 – 11 October 1159) ({{langx|fr|Guillaume de Boulogne}}), also referred to as William of Blois, was Count of Boulogne and Earl of Surrey jure uxoris from 1153 until his death. He was the second son of Stephen, King of England, and Matilda I, Countess of Boulogne.{{sfn|Van Houts|2004|p=112}}

File:Coat of Arms of William I, Count of Boulogne.svg

William married Isabel de Warenne, 4th Countess of Surrey, in 1148.{{sfn|Van Houts|2004|p=112}} After the death of William's elder brother Eustace IV of Boulogne heir to the throne in August 1153, Stephen agreed to name Henry Plantagenet (son of his cousin and rival Empress Matilda) as his heir. In doing so passing over William's own claim to his father's throne with the signing of the Treaty of Wallingford. In the agreement Henry Plantagenet would inherit the throne of England upon Stephen's death and his son William would receive the lands intended for both brothers, making William immensely rich. The treaty ended the Anarchy, a succession struggle between Stephen and Matilda of which both sides were growing weary.

Stephen died in 1154, and Henry initially allowed William to retain the earldom of Surrey jure uxoris (in right of his wife).{{cite book|author=Wilfred Lewis Warren|title=Henry II|url=https://books.google.com/books?id=C8KrkVOxaT0C&pg=PA364|year=1973|publisher=University of California Press|isbn=978-0-520-02282-9|pages=364}} However, Gervase of Canterbury asserts a plot against Henry's life was discovered in 1154 among some Flemish mercenaries. The plan was to assassinate Henry in Canterbury, and allegedly William had knowledge of this plot or was in connivance with the mercenaries. Whatever the truth, Henry fled Canterbury and returned to Normandy.

William had no children. He died in 1159 of disease near Toulouse, and was buried at the Poitevin abbey of Montmorel ({{langx|fr|Abbaye de Montmorel}}). He was succeeded in his county by his sister Marie I. His widow remarried to Henry's half-brother Hamelin.