+---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
William Sprague Trethewy (ABT 1849-15 OCT 1908)
| +---Ambrose Sprague
+---Eliza Sprague (ABT 1824-)
+---Martha Nicholas