William I (born c. 1085 and died October 1129) was the Count of Forcalquier and Marquis of Provence from 1094.
William married Gersende, daughter of Count Guigues III of Albon.
On the death of his father in 1092, he received a part of the parias (tribute) from the taifa of Zaragoza.
His father's will, now lost, enjoined him and his brother Ermengol V, who inherited Urgell, to fight continuously against the Muslims.
[1] William inherited a share of Provence (Forcalquier) on the death of his maternal grandfather in 1094.