Jwhatman: Where are you located? You can update your profile so you don't show as Hopelessly Lost. If you are planning on getting started with bees anyways, you will learn a ton from these very knowledgeable folks!! Welcome, and hope to see you often!
I agree with the others, you have a hive close by. Probably closer than you think. I lose a bee or two every evening, my guess is they are late foragers that get disoriented returning home and fly to the light. I never seem to see bees late, but typically just after sunset, or an hour or so later. We keep our lights dimmed until we're pretty sure the bees are settled for the night, but still lose one or two a night. (Our closest hives are about 25 yards from the light sources)
I find the busiest time around the colonies is an hour or two before sunset when the foragers are returning. I suggest taking your exploration walk then, and they should lead you right to the entrance. Don't discount looking down, too, as at least down here, they are famous for setting up under workshops and sheds. You may get lucky and not need to buy a package or Nuc this year! X:X