Green’s Dictionary of Slang

a fool; thus Jack Adams’ parish, Clerkenwell.

1672		J. Phillips Maronides (1678) V 110: Poor wrinkled weather beaten Madams / led by the noses like Jack Adams.
c.1698		B.E. Dict. Canting Crew n.p.: Jack-adams, a Fool.
1709		N. Ward Compleat and Humorous Account of Remarkable Clubs (1756) 23: What Mortal, that has Sense or Thought, / Would strip Jack Adams of his Coat? [Ibid.] 299: A near Neighbour to St. John of Jerusalem, who at present flourishes his Banner before a noted old tavern in Jack Adams his Parish.
1725		New Canting Dict. n.p.: Jack-adams, a Fool. [...] Jack Adam’s Parish, Clerkenwell.
1737, 1759, 1760, 1776		Bailey Universal Etym. Eng. Dict. [as cit. 1725].
c.1750–1882		B.M. Carew Life and Adventures.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue n.p.: Jack Adams. A fool. Jack Adams’s parish; Clerkenwell.
1809		G. Andrewes Dict. Sl. and Cant.
1811		Lex. Balatronicum [as cit. 1785].
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue [as cit. 1785].
1835		G. Kent Modern Flash Dict. 18: Jack Adams – a muff, stupid fellow.
1848		Flash Dict. in Sinks of London Laid Open [as cit. 1835].
1899		Cornishman 27 July 6/2: Hulver-head, Jack Adam [sic] [...] synonyms in the language of the canting crew, for fool.