E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
By Jingo or By the Living Jingo. Basque Jainko, the Supreme Being. In corroboration of this derivation it may be stated that Edward I. had Basque mountaineers conveyed to England to take part in the conquest of Wales, and the Plantagenets held the Basque provinces in possession. The word was certainly used as a juron long before the Criman War.
Hey, Jingo! What the deils the matter?
Do mermaids swim in Dartford water?
Swift: Actæon (or The Original Horn Fair)
Dr. Morris, in his Historic Outlines (p. 210 note), says it is St. Gingulph, and Professor Skeat (Notes and Queries, August 25th, 1894, p. 149) is of the same opinion. According to The Times, June 25th, 1877, p. 6, col. 1), it is the Persian jang = war, and the juron By St. Jingo is about equal to By Mars. But the word had originally no connection with our jingoism. It was common enough in the early part of the nineteenth century. Query A corruption of Jesus, Son of God, thus, Je-n-go.