So fun fact I learned after not understanding what the heck Chestnut Hill is and trying to (after many years of living locally to it). It is a village. A village typically does not mean much. Or sometimes it does. They can have their own Zip. The Village of Chestnut Hill spans 3 cities (Boston, Brookline, and Newton) as well as 3 counties (the only village to do both those things). It has its own Zip Code, and can be used as an address.
So essentially it is a micro county with no actual authority or reason to exist. If your write Chestnut Hill as your address, which is standard when you live there, that could literally mean 1 of 3 cities. Basically it's nonsense. So it fits right in at Massachusetts
That being said I love the area so much and want to buy there but pricing is too insane for what your get ...