Several people have pointed out that trick or treating isn’t always on Halloween itself.
In some towns, trick or treating always happens on a weekend regardless of when the 31st is.
If your town does that, it will probably be announced through the schools, on the radio, on TV and in the paper. You can also google “[your town] trick or treating”. In some areas the designated time for trick or treating is called Beggars Night.
It’s possible that a few people will show up on Halloween itself, because some people won’t know or will forget.