Roman Catholic Diocese of Helena was formed to serve eastern Montana. The seat of the diocese is in the Cathedral of St. Helena in the state capital of Helena. It was completed in 1914. The bishops of the Diocese of Helena and their years of service: Roman Catholic Diocese of Helena The Diocese of Helena () is the Catholic diocese for western Montana with its cathedral located in Helena, the state capital. The diocese was erected from the year-old Vicarate of Montana on March 7, 1884, while Montana was still a territory. The diocese is a suffragan of the Archdiocese of Portland, which encompasses Oregon,
Helena River catchment Nyaania Creek and on the southern side Piesse Brook are significant in their moving through built up areas which makes them susceptible to urban environment issues. Upper Helena catchment (i.e. above Mundaring Weir) has on the north side of Lake C.Y. O'Connor (formerly the Helena River Reservoir) a range of named creeks that occur in State Forest no 71 and 13: In the higher ground the Helena River passes mainly through State Forest or reserve. This has been beneficial for some of the catchment area, as it has been an important buffer between the urban settlements in the Mundaring