I realize this is an older post, however, it may be of interest to parties searching this part of Montana, to note that Eureka (Located in Lincoln County), currently has no zoning. That said, it is important to understand that restrictions to any given parcel of land, may still be applicable via; covenants, various state and county regulations and other. We are somewhat unique in this regard and that is one of the reasons I enjoy living and working here. :)
Although I didn't answer this specific question, I hope it was insightful for many of you out there, considering Eureka, Montana as your next destination.