Polyamory in 1908
I'm reading an autobiography by "two single ladies" who lived together and shared a bed for their entire adult lives (over five decades). They went to live in a part Northern California where there were few white people. There, they wore "split skirts" and made friends with a local indigenous family (Klamath tribe) that had a wife and two husbands. They observed:
"Of course, if Mart and Essie and Les are all satisfied, it really does seem as though it were their own personal concern. On the other hand, two husbands at the same time would scarcely be tolerated in most white communities." The book is "In the Land of the Grasshopper Song: Two Women in the Klamath River Indian Country in 1908-1909" by Mary Ellicott Arnold and Mabel Reed