Coincidentally while I was working on a post just now about Village Creek, a mid-century modern neighborhood in Norwalk that (or so we were told) was recently listed on the National Register of Historic Places, Gina found a post on Build Blog, with photos of and details about five mid-century modern communities around the country, and a list of six others (nothing about Usonia, in Westchester County, though).
Build Blog highlights Hollin Hills, in Virginia; Arapahoe Acres, in Colorado; Hilltop, in Washington; Six Moon Hill, in Massachusetts; and Krisana Park and Lynwood, in Colorado.
Here's the post. (I helped myself to the photo, which Build Blog says is from the University of Washington Libraries.) - ta