(ABT 1517-ABT 1573)
+---Richard Trethewy (BEF 1550-)
+---Robert Trethewy (BEF 1575-DEC 1623)
| | +---William Hawkins
| +---Joan Hawkins 
(ABT 1530-)
+---Thomas Trethewy (ABT 1596-ABT 1664)
| +---Ann Burgess (-ABT 1637)
+---Robert Trethewy (AFT 1642-ABT 1690)
| | +---William Jolley
| +---Isabel Jolley (ABT 1606-)
+---Charles Trethewy (AFT 1673-DEC 1735)
| | +---John Scawen
| | +---Trehane Scawen (ABT 1614-)
| | | | +---John Trehane
| | | +---Elizabeth Trehane
| +---Dorothy Scawen (ABT 1653-)
| | +---Gregory Arundell (-ABT 1653)
| +---Dorothy Arundell
| +---Edith Crane (-ABT 1666)
+---John Trethewy (ABT 1700-)
| +---Jane Williams (BEF 1683-)
+---Samuel Trethewy (ABT 1726-MAR 1791)
| | +---William Perkin (-1688)
| | +---John Parkin
| | | +---Mary ?
| +---Philadelphia Parkin (ABT 1694-MAY 1783)
+---Samuel Trethewy (ABT 1772-25 DEC 1828)
| | +---Richard Hendra
| +---Blanche Hendra (ABT 1734-JAN 1775)
| +---Jane Murton
+---John Trethewy (ABT 1799-18 OCT 1874)
| | +---William Bryant (ABT 1733-JAN 1796)
| +---Jane Bryant (ABT 1774-13 SEP 1843)
| | +---Walter Lawry
| | +---John Lawrey (ABT 1703-ABT 1799)
| | | +---Julyen Nanjulian
| +---Thomazine Lawry (ABT 1738-)
| | +---John Grose
| +---Mary Grose (ABT 1707-ABT 1757)
| +---Mary Bellamy
+---John Trethewy (19 JUN 1822-28 MAY 1912)
| +---Mary Hawkey (ABT 1798-15 APR 1862)
+---Henry Rowe Trethewy (19 JUL 1851-26 JUN 1924)
| +---Frances Rowe (20 MAY 1822-18 NOV 1898)
+---Hubert Roy Trethewy (13 DEC 1893-10 AUG 1970)
| +---Emily Talbot (15 APR 1862-27 JUL 1943)
+---Maxwell Lindsay Trethewy (08 OCT 1928-)
| +---Elizabeth Margaret Fairbairn Lindsay (06 NOV 1896-07 SEP 1976)
+---Timothy (Tim) Trethewy
| +---M Anne Stevenson
Jamie Andrew Trethewy (31 DEC 1985-)
+---Julie Smith