I would venture to bet that until recently the majority of saunas built in the US have been built by Fins and outnumbered any of the other saunas mentioned. I grew up in a small town that contained numerous distinct cultural neighborhoods. One of them was called Finntown by the old timers. It wasn't derogatory but admiration for the families that migrated to the location and kept their customs. I swear every house built in the beginning of the last century in that neighborhood had a sauna. Dozens must exist still to this day. A lot of people living in them now don't even know it's a sauna. Friends would show me their house and explain they had no clue what the room was about and I tell them sauna. They'd just see it as a shack or extra room with odd paneling and vents to use as storage. Some have been restored tho.