Nobody ever left Ireland to go to America. Pat Naughton left Ballinasloe to go to his cousin John in Roxbury, Boston. James McCurdy went from Rathlin to Lubec, Maine, for a job promised by his mother's uncle. Father Bud Sullivan brought rakes of other Sullivans out from Allihies to work for Marcus Daly in the copper mines of Butte, Montana.
There was no such thing as mass migration, only the accumulation of tens of thousands of individual and family decisions. Identifying and unravelling those decisions can bridge centuries and oceans and re-knit extended families. And the painstaking micro-study of migration clusters is the only way to do that.
There are some excellent individual works – Peter Murphy's Together in Exile (New Brunswick, 1990), a superb reconstruction of migration from Carlingford to Saint John's, New Brunswick, is the founder of the genre and still a shining example. But, as far as I'm aware, no central guide exists to the clustering of Irish migrant origins and destinations. Genealogical anecdotes certainly abound, with dozens of unlikely pairings: Abbeydorney to Westbury; Kilskeery to Charlestown Mass.; Dungarvan to Yonkers. But there is nothing systematic. Perhaps Ireland reaching Out (irelandxo.com) should be encouraging or hosting something like this?
In any case, if you want to have a go for your own locality there are now some excellent online tools.
The indefatigable Steve Morse (stevemorse.org) allows precise reconstruction of Ellis Island origins and destinations – have a look at bit.ly/1tYA0Cq for the 2000 people from Athlone who passed through between 1892 and 1924.
For the mid-19th century, the Boston Pilot "Missing Friends" ads (infowanted.bc.edu) supply even more circumstantial detail.
And the Irish Emigration Database at www.dippam.ac.uk/ied/ is another excellent resource, even if heavily weighted towards Ulster and unfortunately filleted of its 4,500 passenger lists. They languish, unlisted and unloved, in the crude pay-per-view purdah of rootsireland.ie.