It's White Snakeroot! Or, Eupatorium rugosum, or Ageratina altissima. It looks quite a bit like a Boneset, another Eupatorium, but with broader leaves. The pollinators were loving it, so I love it too.
Over at Dean, it's mixed in with all the Crownbeard which is also blooming now. We also have a lot more of it than I realized, which became obvious once it started blooming.
It seems to tolerate dry shady sites well, growing approximately 2-3 feet high. I read that it's poisonous, causing "milk sickness" when eaten by cattle. Maybe that's why the deer don't touch it?
I also found this little gem, identified as Sweet Everlasting, or Pseudonaphalium obtusifolium. It's another plant growing randomly in a wild area that I weeded around earlier. I left it since I didn't know what it was, promising to keep my eyes on it in case it was a non-native. It really is sweet, evidenced by the teeny tiny little ants on it.
I'll have to get back out there and keep looking, there may be more!