Maurice Sendak Memorial Highway in Ridgefield, Connecticut. I'd forgotten that for many years he'd lived there.
It turns out his home and archive will be open to the public next year, though only by appointment. I don't know what will be in the archive, since last year the Maurice Sendak Foundation and UConn announced that a large number of his materials would be "hosted" at the Northeast Children's Literature Collection at UConn, though the Foundation would continue to own them. For what it's worth, I think this is an entirely logical arrangement, since the Children's Literature Collection has the resources to store materials in climate controlled surroundings best suited to preserving them and the staff to provide access to them to scholars and students.
If I'd realized Sendak's house was in Ridgefield, I would have driven by.