When it came to having events recorded, our ancestors were usually not concerned with what jurisdiction they were in. They were generally unaware of changing county lines and other boundaries that would have dictated where they went to have events recorded. Instead, they were more worried about how they were to get where they wanted to go.
In the early settlement period of any area, people used very different means of transportation than what we have today. Horses were common, and a buggy or wagon could have been attached depending on the time period and what kind of terrain was to be traversed. In the frontier regions there was no system of roads connecting towns to other towns, or a town to homesteads further out. Our ancestors occasionally found a "track" that had been worn by early explorers, but by no means was this an easy road. Sometimes they had no "track" at all. In these cases, people usually went to the town that was the easiest and fastest to reach. Because of the difficulty of travel on land, rivers became an excellent alternative mode of transportation. Towns sprang up along rivers as a result.
Although rivers made travel easier, mountains proved to be an obstacle. It was often easier with their wagons or buggies to go around the long way than up and over to a closer settlement.
With an understanding of what the traveling conditions were like for these people, it is easier to see where they may have gone to have events recorded. If an ancestor lived along a river, they probably would have traveled to a place along that river. If they lived in the shadows of mountains, they most likely went to a town that was further away as long as they did not have to go up and over. They typically traveled to the county seat or other larger town that was more accessible to them.
When conducting a locality search, it is helpful to consult a topographical map to determine places they would have probably avoided. You will want to consult a map from the time period your ancestors lived. By doing this, you can rule out certain settlements and determine which towns served as centers of industry and trade, and the most likely to be patronized by your ancestors.
By considering these things, you will get a jump start on the most likely places to search for records that will yield the desired results. When you include the places you should search, you may find that your protractor might not give you such a perfect circle after all.