Green’s Dictionary of Slang

(US) a French-born immigrant.

1755		Caledonian Mercury 28 July 1/2: [reprint from US paper] A Puppet-shew, the Commander of which, Monsieur Jean Potage and two of his principal Officers, were yesterday diverting the populace with their Jeu de Marionettes.
1843		Hull Packet 19 May 3/1: The Circus — Popowitz, the Jean Potage of the arena, took his benefit last night, and was well rewarded.
1899		Record-Union (Sacramento, CA) 12 Nov. 8/3: Jean Potage, a Frenchman, in allusion to his predeliction for soup.
1905		N.Y. Tribune 5 Aug. 8/2: In Holland they [i.e. clowns] are termed ‘Pickled Herrings,’ in France ‘Jean Potages,’ in Italy ‘Macaronies,’ and in great Britain ‘Jack Puddings’.
1983		Maledicta VII 21: Americans borrowed the Continental and British slur Jean potage for our immigrant French.