(ABT 1517-ABT 1573)
+---Thomas Trethewy (-ABT 1616)
+---Bartholomew Trethewy
+---Bartholomew Trethewy (-1666)
+---Bartholomew Trethewy
+---Thomas Trethewy (ABT 1675-MAY 1743)
| +---Jane Bruart 
+---Thomas Trethewy (ABT 1710-FEB 1795)
| | +---Phillip Mellow (ABT 1660-JAN 1711)
| +---Joan Mellow (ABT 1680-)
| +---Jane ?
+---Thomas Trethewy (ABT 1735-SEP 1814)
| | +---Richard Jolliffe
| | +---Robert Jolliffe
| | +---Robert Jolliffe (ABT 1546-1602)
| | +---Henry Jolliffe (ABT 1586-)
| | | +---Thomason ?
| | +---Francis Jolliffe (ABT 1622-)
| | | +---Blanch Pearce
| | +---James Jolley (ABT 1682-APR 1754)
| | | +---Rose May
| +---Elizabeth Jolley (ABT 1713-)
| | +---Richard Osborne (-JUN 1667)
| | | +---Eme Varcoe
| | +---Richard Osborne
| | | +---Joan ?
| | +---Richard Osborne (-NOV 1707)
| | | | +---Arthur Michell (-ABT 1657)
| | | +---Constance Michell (ABT 1635-APR 1717)
| | | | +---Thomas Corne (-1647)
| | | +---Blanche Corne
| +---Blanche Osborne
| +---Bettres ?
+---John Trethewy (ABT 1780-BEF 1861)
| +---Wilmot Hicks (ABT 1731-MAR 1816)
+---James E Trethewy (ABT 1816-)
| | +---John Snell
| | +---Henry Snell (ABT 1700-ABT 1770)
| | | +---Joan Kent
| | +---Henry Snell (ABT 1739-)
| | | | +---John Best (ABT 1648-AFT 1696)
| | | | +---John Best (ABT 1683-)
| | | | | +---Grace John
| | | +---Grace Best (ABT 1713-01 DEC 1799)
| | | | +---Robert Phillips
| | | +---Mary Phillips (17 SEP 1683-01 DEC 1799)
| | | +---Joan Sampson
| +---Mary Snell (ABT 1779-1867)
| +---Jane Martin (-JAN 1839)
+---John Wallace Trethewy (07 MAY 1859-22 JUL 1936)
| | +---Richard Wallish
| +---Jane Wallish (ABT 1822-09 JUN 1897)
James Warren Trethewy (08 AUG 1886-08 JAN 1957)
+---Margaret Adelia Libbey (12 DEC 1859-07 DEC 1943)