'Dagenham' almost certainly means the farm of a man called Dæcca.
In Old English, Dæccan hamm meant the home of Dæcca. The name appears as Dæccanhaam in a Barking Abbey charter dated 666, though other 7th-century dates have been suggested; it records land passing to the abbey from Aethelred, a kinsman of King Saebbi of Essex. The station opened as plain Dagenham in 1885 and became Dagenham East in 1949.