They weren't specified as autistic, because HFA didn't exist when the books were written, but the first characters I recognized as autistic were Maybeth, Liza, and Abigail Tillerman from Cynthia Voight's Tillerman Cycle novels.
Dicey, James, and Sammy might be too. I could never make up my mind.
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"Alas, our dried voices when we whisper together are quiet and meaningless, as wind in dry grass, or rats' feet over broken glass in our dry cellar." --TS Eliot, "The Hollow Men"