| 453 | JACKSON | Millbrook | 19C | |||||
| 010 | JACOB | Falmouth | 18-19C | |||||
| 388 | JACOBS | St. Ives | 1800-1900 | |||||
| 661 | JACOBS | St. Teath | Any | |||||
| 092 | JAMES | St. Just | c1841 | |||||
| 092 | JAMES | Boscaswell | c1841 | |||||
| 321 | JAMES (Thomas) | St. Hilary | 1840-1875 | |||||
| 071 | JANE | Lanhydrock | c1700s | |||||
| 367 | JEFFERY | Gwennap | 17-19C | |||||
| 367 | JEFFERY | Cumberland | 19-20C | |||||
| 424 | JEFFREY | St. Agnes | 1750-1850 | |||||
| 677 | JEFFREY | St. Columb Minor | 1760-1800 | |||||
| 303 | JENKIN | St. Columb Major | 1800-1900 | |||||
| 445 | JENKIN | Gerrans | All | |||||
| 445 | JENKIN | Gorran | All | |||||
| 445 | JENKIN | Kenwyn | All | |||||
| 445 | JENKIN | Perranzabuloe | pre1800 | |||||
| 445 | JENKIN | St. Clement | pre1825 | |||||
| 726 | JENKINS | St. Day | 1800-1860 | |||||
| 195 | JEWEL(L) | St. Kew | pre1725 | |||||
| 239 | JEWELL | Launcells | c1700s | |||||
| 636 | JILLETT | Somerset | All | |||||
| 205 | JOHN | Altarnun | 1600+ | |||||
| 028 | JOHNS | St. Columb Major | c1700s | |||||
| 378 | JOHNS | St. Mewan | 1700-1800s | |||||
| 666 | JOHNS | Veryan | 18-19C | |||||
| 205 | JOHNSTONE | Fifeshire, Scotland | 1700+ | |||||
| 205 | JOHNSTOUN/ONE | Edinburgh | 1600+ | |||||
| 303 | JOSE | St. Stephen in Brannel | 1600-1700 | |||||
| 010 | JOSEPH | Falmouth / Penzance | 18-19C | |||||
| 303 | JUBY | Welbourne, Norfolk | 1750-1850 | |||||
| 666 | JULYAN | St. Columb Minor | 18C | |||||