Coenwulf's kin may have been connected to the royal family of the Hwicce, a subkingdom of Mercia around the lower river Severn.
It appears that Coenwulf's family were powerful, but they were not of recent Mercian royal lineage.
A letter written by Alcuin to the people of Kent in 797 laments that "scarcely anyone is found now of the old stock of kings".
Eardwulf of Northumbria had, like Coenwulf, gained his throne in 796, so Alcuin's meaning is not clear, but it may be that he intended it as a slur on Eardwulf or Coenwulf or on both.
Alcuin certainly holds negative views of Coenwulf, regarding him as a tyrant and criticizing him for putting aside one wife and taking another.
Alcuin writes to a Mercian nobleman to ask him to greet Coenwulf peaceably "if it is possible to do so", implying uncertainty about Coenwulf's policy towards the Carolingians.