1951: First Peanuts Halloween

Linus didn't even exist yet when Charles Schulz' first Halloween-themed comics first appeared in October 1951.  Lucy's little brother wouldn't appear in the comic until 1952.

We can see right off the bat that the October 30, 1951 strip was used as the basis for the scene in "It's the Great Pumpkin, Charlie Brown", in which Violet uses the back of Charlie Brown's head to design her jack o'lantern.  In the original comic strip, though, it was Patty Swanson (not to be confused with Peppermint Patty), who uses Charlie Brown's frowning face, not the back of his head.

This is one of the few instances of Snoopy actually talking:

And apparently, these were the days before costumes became the norm for trick-or-treating, even if it is the day after Halloween...