By the 11th century the evidence suggests Cornwall was an under-populated peripheral territory of the British Isles. However, its population grew a lot faster than that of England in the centuries before the Black Death of 1349. After surviving that shock, Cornwall did rather better economically than elsewhere although its demographic history in the 15th and 16th centuries is still shrouded in some uncertainty. However, we can be confident that after the mid-17th century Cornwall’s early and precocious industrialization led to population growth that was twice as fast as in England. These ups and downs are explained in more detail here.
After 1780, Cornwall’s population continued to grow at around the the same rate as England’s. However, in the 1840s it slowed down as Cornwall’s ‘Great Emigration’ got under way. From the later 1860s the economic diffficulties of the mining industry encouraged even more emigration and Cornwall entered a period of population decline that was to continue for a century, interrupted only by World War Two.
From the 1960s to the present, Cornwall’s demographic experience has been one of the ‘Great Immigration’ as population turnaround in the 60s heralded a massive surge of in-migration from the English heartland and a rise in population. This growth peaked in the 1980s and fell away slowly thereafter, although it continues at an unsustainable level.