Pre-early mid '50s Ivy or trad was largely confined  to Northeastern  upper middle  to upper class WASP communities.
All of the boarding schools and colleges/inivdersities  associated with Ivy are in this area. Where the style flourished outside
this region was in the same demographic enclaves in places like Chicago, San Francisco and the Tidewater of the Southeast.
Of course, there were numerous exceptions . My own father, a first  generation Jewish dentist , always dressed this way, shopping
at Rogers Peet and Brooks unlike most of his peers and my own uncles who wore more mainstream slightly "sharp" clothing. One
uncle was an exception: His elegant clothes were bespoke from D'Andrea Bros. a leading tailor on post-war New York.