Green’s Dictionary of Slang

(Anglo-Irish) the run-down, lowlife area surrounding Montgomery Street, Dublin; also attrib.

1961		D. Behan Teems of Times and Happy Returns 45: Their homes were really situated not in the slums of Monto, but far away on the Pacific seaboard, Sunset Boulevard.
1963		L. Daiken Out Goes She 12: I have seen [...] the invocation and magic of H.O.H.A. fail miserably against brute strength and Monto cunning.
1981		B. Behan ‘The Last of Mrs Murphy’ in After the Wake 18: We were respectable people round this street [...] Down in Monto they had the famine.
1994		(con. 1920s) K.C. Kearns Dublin Tenement Life 68: In them days the whole area was called the ‘Monto’. It was a red-light district.