William de Lancaster I (d. circa 1170), or William Fitz Gilbert, was a nobleman of the 12th century in Northwest England during the Anarchy, and the period during which his region was ruled by King David I of Scotland. His position survived the return of English rule under King Henry II, and his most important lordship, which had previously come together under Ivo de Taillebois, would evolve into what was eventually known as the barony of Kendal. According to a document some generations later, he was also referred to as William de Tailboys (de Taillebois) when younger, and then became "William de Lancaster, baron of Kendal". He died in about 1170.