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There are a number of photos of bits of Galois's notes floating around online, such as here and here. But where are they, physically? I'm hoping what remained of them wasn't tossed out once photos were taken.
At the Library of l'Institut de France that is Bibliotheque de L'Institut de France: "285 feuillets en 27 dossiers. Formats divers. Demi-reliure." There is a research tool online.
Required, but never shown