Whilst compiling my tree I have come across a number of villages that contain at least two families with the same surname but have been unable to establish a link. Is it likely that they are related or is it just coincidence.
Of course, the further back you go the more likely you are to get common ancestors because people did not move around so much as now, and there were less people in total.
One way to look at this is to go onto the familysearch.org site, click on the IGI, put a search in for the name in that county and see what the earliest entry comes up as in that area , then work forward to see how it grows in numbers. It's like an upside down pyramid, you can often guage if they are going to all come from the one early entry. It is probable that the parish registers for the villages are included in the IGI, and so it would be an interesting exercise.