What is the difference between a county shelter and Humane Society?

Humane society are no kill while a dog pound will kill the animal

Actually that is wrong, Humane Society's do kill, you would have to check with the individual Humane Society to find out whether they kill or not. Not all pounds/shelters kill either, many are working towards a no kill approach, which is good as long as animals are not left waiting for years in a kennel. Most shelters/pounds work with rescue groups to get the animals out but some do not and will not. That is when you start getting into the political game that some heads of Animal Control play, they don't want to be questioned or challenged on their practices of killing, so they ban rescues.