Fall Already?

The leaves on our young red oak tree turned bright red, then brown and then fell off - in August. And although we are expecting cooler temperatures this weekend, it's not fall yet. I think the tree died. How can I be sure? Do we wait until next spring to see? I don't see any buds. This poor tree, it fell over in a storm two years ago, and all the time we've had it, it's hardly grown.