Green’s Dictionary of Slang

(US) salt cod; a codfish dinner.

1837		Court Reports in Boston Morn. Post 152: Ducks! why, neither the fowls of the air, nor the fish of the sea, are to be found in the dingy cook's bill of fare—nay, never a Cape Cod ‘turkey’finds its way into his huge caldron.
1856		Wkly Indiana Sentinel (Indiananpolis, IN) 3 July 2/5: The Know Nothing Convention [has] ‘come off’ with a ‘Cape Cod Turkey’ and a ‘Connecticut goose’.
1865		C. Nordhoff 1 May [letter] A salted cod fish is known in American ships as a Cape Cod Turkey [F&H].
1877		Dly Astorian (OR) 11 Nov, 2/1: The parson [...] found on the table not a choice of a two-legged biped but a Cape Cod turkey - that is, a boiled salt cod-fish.
1882		Sydney Sl. Dict. (2 edn) 2: Cape Cod Turkey - Salt fish.
1887		Columbus Jrnl (NE) 23 Nov. 1/6: Their thanksgiving dinner of boiled codfish and potatoes [...] 'It's Cape Cod turkey!' exlaimed Master John MacMoffat.
1890		N.Y. Herald 3 June n.p.: ‘Newfoundland Fishery Dispute’ Factories have been established for the production of Cape Cod Turkeys; i.e. salted cod fish [F&H].
1895		Crowe Aus. Sl. Dict. 15: Cape Cod Turkey, salt fish.
1897		Sun (NY) 7 Mar. 4/6: 'Cape Cod Turkey' still so-called in many pats of New England, the ever-ready and inexpensive codfish.
1900		Reno (NV) Eve. Gazette 28 Apr. 2/2: It is true that we have the ‘Cape Cod turkey,’ which is a codfish, and numerous other humorously applied special dishes.
1907		J.W. Carr ‘Word-List from Hampstead, N.H.’ in DN III iii 183: Cape Cod turkey, n. phr. Salt codfish.
1913		Nottingham Eve. Post 22 Sept. 3/4: Salt fish generally is known as ‘Cape Cod turkey’.
1919		Free-Trader Jrnl (Ottowa, IL) 8 Dec. 7/3: Gastronomic Animals [...] The only American samples that can be offered are the Albany beef and the Cape Cod turkey (codfish).
1922		Eve. World (NY) 13 Jan. 34/6: 'Marblehead turkeys' is a name sometimes facetiously given to cod-fish in Massachusetts. Those caught in the vicinity of the Cape are 'Cape Cod turkeys'.
1926		Wood & Goddard Dict. Amer. Sl.
1946		S. Hibben Cookery 71: ‘Cape Cod Turkey’ (Stuffed Codfish) [DA].
1960, 1975		Wentworth & Flexner DAS.
1989		H. Rawson Dict. of Invective (1991) 289: Cape Cod turkey, a tongue-in-cheek euphemism for dried salt codfish, and one of a large subset of place names that have been used to flavor different foods.