It was originally a 1941 book by Mary O'Hara set in Wyoming. Actually, it was quite a good book, but a movie was made of it in 1943 that was atrocious. It was the first movie for a child actor who went on to stardom; Roddy McDowell. His English accent just didn't fit the high plains of Wyoming, but it was a pretty bad movie otherwise as well. The TV series came much later...