(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 ?
+---John Trethewy (ABT 1741-)
| +---Grace Rickard
+---Richard Trethewy (ABT 1774-)
| | +---Francis Honey
| +---Elizabeth Honey (ABT 1742-)
| +---Ann Johns
+---William Trethewy (ABT 1814-)
| | +---Alexander Bone
| +---Rebecca Bone (ABT 1777-)
| +---Rebecca Boney
+---Jabez Trethewy (12 MAR 1851-1935)
| | +---Nicholas Williams
| +---Martha Williams (ABT 1809-BEF 1890)
| +---Frances ?
+---William Thomas Trethewy (03 SEP 1893-04 MAY 1956)
| | +---Thomas Wallis (ABT 1826-)
| +---Mary Wallis (29 NOV 1855-16 FEB 1944)
| | +---Charles Phillips
| +---Christiana Phillips (ABT 1834-)
| +---Catherine ?
+---Allan William Trethewy (30 OCT 1916-)
| +---Ivy Louise Harper (1893-)
Bruce Trethewy (1951-)
+---Elizabeth Maude Ebert