I'm running into a similar problem in two different works, so I have two settings:
1. unspecified location on Maryland's eastern shore, most people earn money by fishing or by taking tourists out to go fishing/hunting
2. totally made up universe, but fairly similar to most modern Western countries in terms of mobility and differences between rural and urban areas (higher mobility and transience in urban areas), coincidentally also a town where the economy is mostly around fishing, but no tourism
Basically what I want to know is, how big can a population get and still have everyone know everyone else at least by sight (perhaps just "that's one of the Smith children")? And of course, the flip side of that is, being able to know that someone is not a local even if they're not giving off any non-local vibes--you don't recognize them, ergo they must be from someplace else.
In both cases, the same people are living there for generations, with very few people moving in, and some people moving away.
As far as the eastern shore question goes, I've looked at a map and found several locations that might fit between 800 and 1000 in population, and from what I've read, although there is a significant amount of tourism, there's not a lot of moving in and out of these areas--most people who live there grew up there. Would people in a town of this size instantly know that someone wasn't from the town?
My gut instinct is yes, but on the other hand, my high school was about 800 students, and I didn't know everyone there by sight--not even close. I didn't even know everybody in my grade. I'm finding it difficult to conceptualize what the difference is between a city of 100k and a city of 200k, let alone what the difference is between a town of 500 and a town of 1000. Taking two places near where I grew up, I would have guessed that Easton and Bethlehem were about the same in population--turns out that Bethlehem is almost 3x the size of Easton, 70k to 25k. So trying to set population numbers for places always feels like a game of Wild Mass Guess to me.
Ideally I'd like to hear from people who grew up in towns where "everyone knew everyone by sight", and what the population was of your area. It doesn't really matter where in the world you are from because like I said one of the stories is set in a different universe.
As far as Googling and looking things up, I have asked some people who have visited the eastern shore what they thought of the communities. I have tried to look up populations for places near where I grew up and where I live now, figuring that I would be able to say "Oh, so a place with X people is like Z", but like I said, I'm quickly realizing that the size that I think places are in my head bears no resemblance to reality. Easton and Bethlehem feel so similar to me that I just assumed they had similar populations, but it's not even close. On the other hand, Allentown feels a lot larger, and while it is larger, it's closer in size to Bethlehem than Bethlehem is to Easton.
tl;dr I'm going to have characters say things along the lines of "I grew up in a town of X people and back there everyone knows you and your mom and your little dog too" and have the number X be reasonable. Would this be reasonable in a town of 800ish?