+---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
+---John Trethewy (25 DEC 1805-1871)
| +---Catherine Scholier
+---Alexander Thomas Trethewy (16 AUG 1842-09 AUG 1901)
| +---Margaret Grinton (24 APR 1810-1860)
+---Harry Ira Trethewy (27 SEP 1878-1932)
| | +---James Trethewy
| | +---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)
| +---Anna Maria Trethewy (-20 SEP 1900)
| +---Ellen Chesley
+---Leslie Horton Trethewy (22 DEC 1908-27 DEC 1975)
| +---Bessie Jane May Horton (19 OCT 1887-27 JAN 1968)
Horton Trethewy (12 JUL 1944-)
| +---James Trethewy
| +---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
+---Bernice Trethewy (JUN 1902-02 DEC 1958)
+---Hattie Dean Archibald (15 NOV 1875-08 JUL 1960)