JamesHerriot.org
A blog about all things James Herriot: his life, his works, the TV show and movie based off his work, and more.
All Creatures Great and Small
https://us.macmillan.com/allcreaturesgreatandsmall/jamesherriot/9781250057839/
The official American publisher, Macmillian, has their own website about the book.
Thirsk Tourist Information
https://www.visitthirsk.org.uk/pages/jamesherriot.php
Thirsk, the place where James Herriot called his home, has information about James Herriot, as well as their James Herriot Museum, on their site.
Darrowby, the setting of the book, is loosely based on Thirsk.