The population in most areas of Dutchess County is growing, so it would probably be safe to say that Dover Plains is growing as well. It couldn't possibly be growing at the same rate as the Poughkeepsie area, though, which has been steadily booming for years now. Dover Plains is still a small village when all is said and done, and that hasn't changed.
Unfortunately, Census data is not as specific as we'd like it to be when it comes to Dover Plains, so we don't have any definitive answers, but in my opinion it is probably slowly growing. One website with town population estimates suggests that it has, in fact, increased in population over the last decade (by more than I figured, but they're just estimates). To me, however, it still looks about the same development-wise as it did 10 years ago, so I suppose that's something.
