Thomas Trethewy (ABT 1803-04 APR 1849)
| +---James Trethewy (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 ?
| +---James Trethewy (ABT 1742-MAY 1824)
| | | +---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 ?
+---Grace Trethewy (ABT 1780-)
| +---James Trethewy (ABT 1517-ABT 1573)
| +---Thomas Trethewy (-ABT 1616)
| +---Bartholomew Trethewy
| +---Bartholomew Trethewy (-1666)
| +---Bartholomew Trethewy
| +---Thomas Trethewy (ABT 1675-MAY 1743)
| | +---Jane Bruart
| +---William Trethewy (ABT 1712-JAN 1777)
| | | +---Phillip Mellow (ABT 1660-JAN 1711)
| | +---Joan Mellow (ABT 1680-)
| | +---Jane ?
+---Elizabeth Trethewy (ABT 1749-)
+---Grace Rickard