William de Lancaster I

William de Lancaster I, or William Fitz Gilbert, was a nobleman of the 12th century in Northwest England. 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", although there is some uncertainty amongst most commentators concerning the exact meaning of the term "baron" in this case. He is the first person of whom there is any record to bear the name of Lancaster and pass it on to his descendants as a family name. He died in about 1170.

Despite his surname, William and his relatives appear in contemporary documents relating mainly to what is now the modern county of Cumbria, not Lancashire, especially Copeland in western Cumberland, Furness in the Lake District, The Barony of Kendal, which became part of Westmorland, and various areas such as Barton between Kendal and Ullswater, also in Westmorland. Much of this area was not yet permanently part of England.

Although only part of this area was within the later English county of Lancaster or Lancashire, this entity had not yet come to be clearly defined. So the title of "de Lancaster", by which William is remembered, could have referred not only to the church city of Lancaster, to the south of this area, but to an area under its control. In 1900, William Farrer claimed that "all of the southern half of Westmorland, not only the Kirkby Lonsdale Ward of Westmorland, but also the Kendal Ward, were linked with Northern Lancashire from a very early time" and formed a single district for fiscal administrative purposes.

The two apparently lost records which are said to have mentioned William's father Gilbert also apparently connected him to Cumbria, specifically to the area of Furness.

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