We can really open up Pandora's Box if you want to. You haven't heard anything from the city because Halloween is non-government holiday. They won't regulate how we observe a holiday. It is not even a Utah thing. It is, however, a neighborhood thing. Here in South Jordan, particularly Daybreak, the majority of families will be celebrating this holiday on Saturday. Primarily because most LDS families here choose to spend their Sabbath at church, at home, and with family. Who knows, they might even have a special Halloween themed Sunday dinner. They just don't trick-or-treat on Sunday.

I would bet that most families in Salt Lake proper and in Sugar House will probably get the bulk of their trick-or-treaters on the 31st (the TRUE holiday). Largely, because there is a lower % of LDS families in those communities than here in South Jordan. It is personal and it is up to you how you want to celebrate.