The NY, Housatonic and Northern did some work in Westchester and the Northwest corner of Greenwich CT. This work was mostly done in 1867-1868. Old maps of North Castle (NY) and Greenwich show the proposed route. You can still see the work today.
I was in the Chappaqua Library a week ago and looked at North Castle history. There was a picture of the Housatonic grading that had been done in Greenwich on Sterling Rd. (still a private road) I do not know why the company was working in the middle of the proposed line in CT, but it may have had something to do with preserving their CT charter.
If you do a Google map search for 760 Riversville RD and go to the "hybrid" map, you will see the remnants of the roadbed work to the west of Riversville Rd. This grading continues to Bedford Rd in Greenwich. (Part of the original Post Road from NYC to Bedford and north. What you see on the map is a fill and can be clearly seen today.
The line was to enter CT just north of the Westchester County Airport, cross Bedford Rd, Riversville Rd, Sterling Rd and then re-enter North Castle at Creemer Rd, just inside the NY State line. I believe this was to be the location of the Armonk Station. I do not know if a station was planned for North Greenwich.
Parts of the work were obliterated by the Tamarack Country Club.
Try this link. Click on the link then select JPEG. Then go click the upper left of the map to see the proposed route. You can click to enlarge for better detail.
http://magic.lib.uconn.edu/cgi-bin/MAGI ... s32.unkn.1
There is an 1868 North Castle map that shows the sections on either side of Greenwich. I have the map but will try to find a link.