I vote to drop it off at animal control. If it's well fed, it could be a neighbor's pet. Perhaps they let it out for rodent control. If you have chickens, you likely have rodents, the cat could have wandered in after anything, chicken, mouse, wild bird. The neighbors will have to claim it, likely pay a fine to spring it from the pound, hopefully learn a lesson about letting their cat wander. If they don't claim it, it will either be put down or re-homed, in both these situations the cat will no longer be your problem.