During the 1970s, the energy crisis came to the forefront and some states voted to add Daylight Savings Time to conserve energy. Most of the continental U. S. has since adopted this law except for some areas in Indiana and a very small segment of Arizona. There may be others for which I am not aware.
As has already been pointed out, Indiana has since gone to DST.
But I always found it fascinating how sometimes people would get the situation almost, but not quite right. It wasn't a question that there were a few areas that didn't observe DST. It was the opposite- there were only a few that did. Only 14 of the 92 counties in the state changed their clocks. But I once had some woman who had never set foot in Indiana argue with me about it.
Sadly, Mitch Daniels pushed the DST legislation through a number of years ago. I was so bummed. I hate DST.