I am not a specialist on the town system, so don't expect any precise answers but... According to Wikipedia, the village with the biggest population is 読谷村 in Okinawa which has 39,733 people. the village with the smallest population is 葛尾村 in Fukushima which has, surprisingly, 18 people. It seems to me that the population doesn't matter to whether the place is called 村 or not. It may be related to its history, I suppose. Hope this piece of information helps you a bit. Any language feedback is welcome!