Family name Postlethwait (Postlethwait 
) , across the world, is a rare last name. The family name Postlethwait is habitual in the United States, where it is a rare surname, New Zealand, where it is a very rare surname, and Canada. Measured by absolute frequency, it most frequently occurs in the United States, Canada, and the United Kingdom.
| VARIANT | COUNTRY |
|---|---|
| Postlethwait | United Kingdom, United States, Canada, Brazil, New Zealand |
|
john postlethwait American biologist (b. 1944) |
|