My wife's first thought was Imperial as well, but I haven't found a match in online catalogs, etc. Initial searches concentrated on the more well known milk glass companies... Westmoreland, Imperial, Mosser, Dunbar, Fostoria, Fenton, etc., without much luck. We think it's old, at least depression if not earlier.
Nothing in the Milk Glass Society gallery that matches? http://www.nmgcs.org/
Thanks for the link. I've been there before but not gone through all the galleries. Will get back there.