We were using holocaust to describe the Nazi genocide back in the sixties when I was a teenager in Montgomery County Maryland. I first encountered the term when a friend's mother gave me the book "Holocaust Kingdom" by Alexander Donat which was published in 1965 and is a surprisingly uplifting account of the author's journey through the terror. She was from Poland and survived the camps but most of her family did not. I don't think the term came into wide usage in the U.S. until some time in the 70's after the airing of a TV movie about it.