Diogo Fernandes (died before 1 December 928), (Spanish: Diego Fernández) was a count in the Kingdom of León whose filiation has not been documented although, from his patronymic, it is known that his father was named Fernando, and that he was possibly from Castile. He is the ancestor of many of the important 10th and 11th century noble families in the County of Portugal and in the Kingdom of León. Although the relationship has not been documented, some authors believe that Diego could have been the brother of Count Ero Fernández and of Gudesteo Fernández.