Green’s Dictionary of Slang

a religious dissenter, typically a non-conformist or Presbyterian; also as adj.

c.1698		B.E. Dict. Canting Crew n.p.: Non-con, one that don’t conform to the Church of England.
1707		Humours of a Coffee-House 26 Dec. 79: When a Parson meets him in the Street [....] and if he’s a Non-Con, he’ll kick him into the Kennel and Piss upon him.
1723		C. Walker Authentick Memoirs of Sally Salisbury 102: He is no better nor worse than an Eminent Non-Con Parson, Lusty and Lustful, who oft leaves his Flock to regale himself in Masquerade with persons of your Sex and Function.
1731		C. Coffey Devil to Pay I ii: A plaguy Non-con Parson worse than all.
1748		R. Dodsley Collection of Poems I 66: Said a formal non-con [...] come, be of our sect, For then you are safe, and may plead you’re elect [F&H].
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1843		C. Robinson in Diary (1872) 7 Apr. ii 239: So it is that extremes meet, and that we non-cons are in accord with the High Church divines [F&H].
1914		E. Wittmann ‘Clipped Words’ in DN IV:ii 126: non-con, from non-conformist.