Hi there,
There is not a formal geocaching group in Butte that I am aware of, Jaxonlee, but there is a fairly active one just down the road in Helena. The call themselves the Capital City Geocachers, and they are actually having an event later this month. Here's a link to the listing for the event: http://www.geocaching.com/seek/cache_details.aspx?guid=6cb00547-0caf-4bf7-a8c7-ba61a3e1c4fd
Another useful resource might be the Geocaching Montana group on facebook. It's run by a cacher out of Great Falls, and there are a number of Montana geocachers subscribed to it.
I hope this helps!
Sincerely,
MsDelilah
Volunteer geocaching.com cache reviewer MT/ID