The wikipedia page X rating https://en.wikipedia.org/wiki/X_rating lists The Evil Dead as one of main stream films that received an X rating but the wikipedia page for The Evil Dead doesn’t state it was X-rated.
I saw The Evil Dead in the theatre during its first run. I was 12. My hometown theatre owner didn’t enforce restrictions on R rated movies. He just cared about the money for your ticket. But X rating? I doubt an X-rated film would even be shown at all in my Kansas home town. I’m sure if it had been rated X I would have known and remembered it.