+---Richard Trethewy (ABT 1665-JAN 1741)
+---William Trethewy (ABT 1694-)
| +---Ann Martyn 
(ABT 1666-JUN 1738)
+---James Trethewy (ABT 1719-)
| +---Jenefer Sweet (-SEP 1733)
+---James Trethewy (ABT 1746-)
| +---Grace Warne
+---George Trethewy (ABT 1783-05 DEC 1853)
| +---Elizabeth Carpenter
+---William Trethewy (ABT 1825-14 APR 1871)
| +---Elizabeth Roberts
+---Lewis Trethewy (ABT 1861-)
| | +---Ambrose Sprague
| +---Eliza Sprague (ABT 1824-)
| +---Martha Nicholas
William J Trethewy (DEC 1898-)
+---Elizabeth A ? (1860-)