Green’s Dictionary of Slang

(Aus.) a Justice of the Peace.

1849		Bell’s Life in Sydney 10 Feb. 1/1: I begged Papa to take me and was joined by a Gentleman Papa called a J.P. - I don’t know what profession he may be but I suppose he is a judge of Pigs as I heard him offer Papa some Bacon.
1863		Goulburn Herald (NSW) 21 Jan. 3/2: Of course such a notable character must be a J.P. I do not mean judge of pigs, but a real magistrate.
1864		Launceston Examiner (Tas.) 12 Nov. 5/2: The proprietor, not knowing by whom the pigs were fed, affixed large tickets to them, intimating that they came from ‘I. Donahoo, Esq, J.P, (judge of pigs) of Nowhere Hall.’.
1874		Queensland Times (Brisbane) 6 Aug.3/3: For this charming night’s lodging, and a rough feed, he got his host made, ’tis said, a J.P. (judge of pigs), much to the annoyance [...] of the whole district, who remonstrated against it.
1884		Argus (Melbourne) 13 Feb. 6/4: Councillor Redfearn gave Councillor Greenhill the title of ‘judge of pigs,’ referring to his J.P.-ship.
1886		Kyneton Obs. (Vic.) 1 June 2/6: The poor aspirate received very rough treatment from her, and she spoke of being arranged (sic) before ‘judges of pigs’.
1907		N.F. Spielvogel Cocky Farmer 12: There was a whole lot of chaps already there. Bill Smith, Joe Brady, [...] and Mick Long and Judge of Pigs - you know his name was Mister James Lacey Jay Pee; but us chaps called him Judge of Pigs for short.
1934		Dly News (Perth) 24 Apr. 4/6: Seventeen pages of the ‘Government Gazette’ last week were taken up with the publication of the names of those distinguished gentlemen amongst us who hold what is known as the Commission of the Peace - in other words, of our J’s.P. (not judges of pigs, as a schoolboy once answered an examination question).