Although there was not and is not any Brooklyn neighborhood that was officially named “Irishtown”, we know that in articles like the Whiskey Wars that we previously read that areas like Vinegar Hill, DUMBO and the Brooklyn Navy Yard were referred to Irishtown because of the Irish immigrants that came here in the 19th century.  Eamon Loingsigh was informed about “Irishtown” through his elderly relatives who had family who had lived in those areas and experienced life in these Brooklyn neighborhoods.  I think with word of mouth information given to Eamon Loingsigh based on his family history, this was the base for the research he needed for his book on Irishtown, and he used these historical stories to branch out and dig deeper with secondary sources to find more.