This is a good question! In I Heard the Owl Call My Name, by Margaret Craven, the story focuses so much on the whole village that it can be hard to know who the main character is.

But as you move along in the story, you see how it starts to revolve around Mark Brian, the young vicar sent by his bishop to the village. So, Mark Brian is the main character. Throughout the novel, Mark struggles to understand the people and culture there, to gain their trust, and to deal with his own illness.

You might argue that there is no main character in this story: that it's about the villagers as a whole. One way to counter that argument is to look at who undergoes a transformation. Who changes? Who learns something important that he or she never expected? It's Mark. For that reason, even if he didn't appear on every page, you could still call him the main character.