Sunk Island originated as a sand bank in the Humber Estuary; at first it was open sea, then accumulated until visible only at low tides, then at all tides. Colonel Gilby raised the outer banks, making it useful for pasturage, under lease/gift from the crown.
By the reign of Charles I of England, it was said to form a seven acreisland, one-and-a-half mile from the mainland. From 1663, the land around it was gradually drained, and by the mid-18th century, the channel separating it from the shore had entirely silted up. It was parished in 1831.