What zombie movie is this?

I watched it as a kid, but not too young, so probably mid 80's, but the
movie may have been older. Anyway, it takes place in a very rural,
"backwater" setting. I remember a scene with a sheriff watching a young
lady skinny dip (hey, this sort of stuff makes an impression on a young
boy!) while zombies "sneak" up on him. Another scene where an older lady
comes out of her house looking for her son or husband "Jimmy", carrying a
shotgun. Both are of course killed by zombies. This is about all I
remember.

I think this may have been the first "zombie" movie I ever saw and I'm
trying to track it down again. I've seen you guys work wonders with less
than this! Can you help me out?

James.