Anecdotally, I know a few people from the Edgemont area. There were quite a few Indian kids at their high school, although not nearly as many as you'd find in Plainsboro or Edison.
IIRC, there was a fairly large Japanese population in Edgemont/Scarsdale at one point. Not sure if that's still the case.
There are a lot of Japanese in Edgemont/Scarsdale/North Eastchester. All of them are expatriates.
This is the drill: A lot of established Japanese firms send their up-and-coming future middle management men (yes, they are all men) to work in their NYC office for 4-5 years. They are sent right around the time when their children are around 5-6. The basic idea is that this is a benefit that they get to live the USA upper-middle-class lifestyle for 4-5 years while their children get to learn English.
Of course, it is critical that they return to Japan before their children attend middle school. If their children attend middle school in the USA they will be different enough from their Japanese counterparts that when they do go back to Japan it will be noticeable to their peers. In Japanese schools, just like in society at large, being different is the kiss of death.
There are a bunch of Japanese relo firms that bought out a bunch of houses in the Edgemont/Scarsdale/North Eastchester area and they rent them out to firms who then give them to the expatriate Japanese family. I have several houses like this in my area and I see the 4-5 year turnover of Japanese families. These Japanese families know they are guests and are very courteous and respectful of their neighbors. There is nothing better than to have a Japanese neighbor. My son become friends with some of their children and it was sad when they started to go back to Japan a couple of years ago.
The Japanese men go off to work in NYC early in the morning and come home late (just like in Japan.) The Japanese wives/mother, being Japanese, organize into groups. In the schools, there is a separate Japanese PTA which is much more organized than the regular PTA which is already staffed by various tiger moms. The Japanese tiger moms take it up to another level.
When my son was in elementary school there were a large number of Japanese students when you add up the various Chinese and Korean kids often formed 30% 40% or even 50% of the classes. Once my son started to attend middle school (this year) the number of Japanese students collapsed for the reason I stated above.