The Montana Chapter of the
International Dark Sky Association

May of 2019 saw the formal establishment of the Montana Chapter of the International Dark Sky Association.
The Montana IDA Chapter is dedicated to protecting the state's heritage of star-filled night skies.
From its website:
"The chapter is an all-volunteer, educational group working with businesses, towns, municipalites, groups and individuals to keep our rural night skies dark and full of stars, and to help Montanans tackle light pollution issues in our towns and cities."