Cornish surnames such as Chesterfield, Oxnam or Sturtridge hail originally from places well outside Cornwall. Their presence, sometimes for centuries, indicates that the horizons of people in the past were not confined entirely to their own small patch. Unlike the common misconception, this was a society on the move, although not usually the distances implied by the names above.
Short distance migration from parish to parish is shown by the turnover of surnames in any single parish. Compare my lists of the most frequent surnames in the 17th and 18th centuries and you’ll immediately see that.
Take Probus, a farming parish on the main road between Truro and St Austell. In the Protestation returns of 1641/42, there were 156 separate surnames in the parish. Of these only 53, or a third, were also found in the marriage registers of the mid-1700s. By the time of the 1861 census this had fallen to a quarter. Moreover, some of those had disappeared in the 18th century only to return in 1861, for example Emmott, Hearle and Scawen. Fewer than one in five of the surnames present in Probus in 1641 were also there in both the 18th century and 1861.
| Persons | Surnames | |||
| 1641 | 1730-80 | 1861 | ||
| 1641 | 292 | 156 | 53 | 37 |
| 1730-80 | 298 | – | 171 | 69 |
| 1861 | 302 | – | – | 160 |
The slightly lower proportion of surnames that appear in both the 18th and 19th centuries (at 31%), when compared with the 34% present in both 1641 and the 1700s, may hint at an increased level of mobility over time, but the difference is relatively small and suggests the turn to a industrial society had little impact on a non-mining parish. The picture may, of course, be quite different in the mining districts.
Cornish studies resources 
I am afraid I don’t understand the left column on the table and how the bottom two rows relate to the surname data.
Can you clarify whether women had their own surnames at the times described eg 1641 and whether the gradual loss of surnames could reflect an increasing tendency for women to adopt their husband’s surnames upon marriage?
I am not sure also when surnames became common.
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Sorry if it wasn’t obvious. The left column is the date of the list of surnames examined. The second column is the total number of persons on each list (In 1641 and the 18th century this is men, for 1861 it’s household heads. The next column to the right will show the number of separate surnames present at each date. Thus the 292 persons in 1641 shared 156 separate surnames. Of these 53 were still present in the 18th century and 37 in 1861, showing that 103 and 119 had disappeared at each point in time.
By this time women were usually taking their husband’s surname on marriage.
For the history of surnames see https://bernarddeacon.com/cornish-surnames/where-surnames-come-from-a-brief-history/
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