Is there a way to find out how crowded a place can be during certain period?

This might be a very dumb question, but I love to visit places which are not very crowded. For example, I am looking for some place, preferably on the sea, to visit in the first part of September (in Europe). There are quite a few options that I can afford, but I was wondering if I could somehow find out if those places are usually crowded or not in September. Is there any way except raw Google searching to do that? I mean, I doubt there is some tool/application for that, but some tricks you might know? Or some database, something like that?