It could be that there was minor evidence that we never noticed.  However, we would have noticed digging around the run area, and we definitely didn't see that. 
My neighbor kept his feed outside in a weather proof container.   He indicated that a coon had gotten in it a couple of times.  So, it is possible that a coon set up shop somewhere nearby to access the feed.   My other neighbor has had a coon wipe out his sweet corn that he was growing, and seems to have been eating his strawberries.   I'm not sure exactly where a coon lives - the only habitat I'm aware of is in the hollow of a tree, but surely they live in all kinds of habitats that are relatively dry and dark, as they flourish in suburbia and do fine in cities - without hollowed out trees!  So, my two neighbors have more cover near to them than I do, which is why they may have had signs of coons before me.    But now that the coons got a taste of chicken dinner, my flock is the nearest source as they depleted my neighbor's flock.