The counts of Nantes were originally the Frankish rulers of the Nantais under the Carolingians and eventually a capital city of the Duchy of Brittany. Their county served as a march against the Bretons of the Vannetais. Carolingian rulers would sometimes attack Brittany through the region of the Vannetais, making Nantes a strategic asset. In the mid-ninth century, the county finally fell to the Bretons and the title became a subsidiary title of the Breton rulers. The control of the title by the Breton dukes figured prominently in the history of the duchy. The County of Nantes was given to Hoel, a disinherited son of a duke. He lost the countship due to a popular uprising. That uprising presented an opportunity for King Henry II of England to attack the Breton duke. In the treaty ending their conflicts, the Breton duke awarded the county to Henry II.
Alan I, King of Brittany ruled Nantes as King of Brittany until his death in 907.
The County of Nantes was merged permanently into the Ducal crown of Brittany, and subsequently the crown of France, through Constance's descendants.
