I have to jump in to say that I think there's some confusion about what chapter books are, based on some of the examples given.
In my experience, chapter books are indeed books with chapters, but they are intended for kids who are moving on from easy/early readers and not yet ready for middle grade novels, two categories which may also have chapters. They tend to be but may not always be episodic (each chapter is its own story) and not have the complete story arc of a novel.
So, I would place Island of the Blue Dolphins and Where the Red Fern Grows firmly in the middle grade novel category. And I would place Henry and Mudge and Frog and Toad in easy reader. Pippi Longstocking I'm not sure about, but without re-reading it I think I'd place it as a younger MG novel, but I could see a case for chapter book too...
Other books to add to the chapter book stack: the Time Warp Trio books, and the Ivy and Bean books.