Dr. Suess is still the earliest cite, 1950.
There is a cite from October of 1951, from Newsweek, which says
In Detroit, someone who once would be called a drip or a square is now, regrettably, a nerd, or in a less severe case, a scurve./QUOTE]
Some professional etymologists think that the “nerd” used by Seuss was perhaps influenced by the character “Mortimer Snerd,” a dummy used by Edgar Bergen, an incredibly well-known and popular ventriloquist from the 1940’s.
Many professionals also believe there may have been a totally independent coinage of the word in the 1940’s having nothing to do with Seuss(but perhaps something to do with Snerd).
As newspapers and other print materials become increasingly digitized and available to scholars, someone may find that term used before Seuss. I’ll try to keep you up to date.