+---Richard Trethewy (ABT 1665-JAN 1741)
+---William Trethewy (ABT 1694-)
| +---Ann Martyn 
(ABT 1666-JUN 1738)
+---James Trethewy (ABT 1719-)
| +---Jenefer Sweet (-SEP 1733)
+---William Trethewy (ABT 1753-)
| +---Grace Warne
+---Richard Trethewy (02 FEB 1799-24 DEC 1875)
| +---Catherine Scholier
+---John Trethewy (25 JUL 1823-24 SEP 1876)
| +---Catherine Hooper (25 MAR 1796-06 DEC 1893)
+---Charles M Trethewy (-1965)
| +---Margaret Eleanor Ross
+---William Charles Trethewy (-1959)
| +---Hattie Dean Archibald (15 NOV 1875-08 JUL 1960)
+---Peter George Trethewy (-09 MAR 1984)
| +---Marjorie Musgrave
Joyce Trethewy
+---Ethel Frederickson