1086, Cestre Scire, from Chester + scir "district" (see shire). Cheshire cat and its proverbial grin are attested from 1770, but the signification is obscure.
I made a pun the other day, and palmed it upon Holcroft, who grinned like a Cheshire cat. (Why do cats grin in Cheshire?--Because it was once a county palatine, and the cats cannot help laughing whenever they think of it, though I see no great joke in it.) I said that Holcroft, on being asked who were the best dramatic writers of the day, replied, "HOOK AND I." Mr Hook is author of several pieces, Tekeli, &c. You know what hooks and eyes are, don't you? They are what little boys do up their breeches with. [Charles Lamb, letter to Thomas Manning, Feb. 26, 1808]