(ABT 1517-ABT 1573)
+---Thomas Trethewy (-ABT 1616)
+---Bartholomew Trethewy
+---Bartholomew Trethewy (-1666)
+---Bartholomew Trethewy
+---Thomas Trethewy (ABT 1675-MAY 1743)
| +---Jane Bruart 
+---William Trethewy (ABT 1712-JAN 1777)
| | +---Phillip Mellow (ABT 1660-JAN 1711)
| +---Joan Mellow (ABT 1680-)
| +---Jane ?
+---John Trethewy (ABT 1741-)
| +---Grace Rickard
+---John Trethewy (ABT 1776-)
| | +---Francis Honey
| +---Elizabeth Honey (ABT 1742-)
| +---Ann Johns
+---John Trethewy (ABT 1808-11 MAR 1887)
| | +---William Gummow
| +---Mary Gummow (ABT 1776-)
| +---Mary Colman
+---John Trethewy (ABT 1847-14 AUG 1901)
| | +---Samuel Bonython
| +---Jane Bonython (ABT 1810-BEF 1871)
+---James Rowe Trethewy (ABT 1874-03 FEB 1961)
| +---Isabella Rowe (ABT 1844-)
James Eric Trethewy (1913-2000)
+---Ada Maude ? (-04 APR 1948)