I used to live in a town situated in two states, with the state line right down the middle of one of the busy streets. Two city governments, two county governments, two state governments. Two school systems. Two, very different, sets of liquor laws. However, often, folks on one side of the line worked, shopped, went to church or the doctor, died and were buried on the other side. I even saw the weather change dramatically (from pouring rain to blue skies) as I crossed State Line Boulevard.
Now, such a town is highly unusual, but it should remind all of us that arbitrary boundary lines exist on maps and in the minds of county recorders and tax collectors, but do not stop people from crossing and taking care of business in places other than where they lived.
You may discover than one ancestor's family lived, voted and paid taxes in one county, but did not attend any church. Check a plat map to see where in the county the family lived, then check the closest county or counties to see if they attended in a neighboring community. They may have purchased supplies in a town close to them, but not in the county where they lived. Or a sick child might have been taken to a doctor or specialist in a larger town in another community. In the 20th Century, it became more common to take a sick family member to a hospital in the largest city in the area, where the patient might have died, leaving no legal death record in the county of residence.
So take a few minutes to seek your ancestors where they didn't belong. You might discover some new information!