There's 3 big waves of Irish emigration to the U.S., 18th century to the point that maybe a third of the American colonists had some Irish heritage (and a distrust of the English that certainly helped rebellion) but that includes a lot of Scotch Irish both for better land prospects and as border defenders as James Webb discusses in his book "Always Fighting."
The big wave around the 1840's potato famine when millions of left Ireland, mostly Catholics with a higher share of Gaelic speakers because that was the population England's political hierarchy refused to help and considerably exacerbated the emigration and death toll. I think that's what you're referring to. There's a long subsequent emigration from the Civil War (cannon fodder for Union regiments) into the 1890's which drew from across the country including city and better educated "lace-curtain" Irish and distributed them more across America instead of congregating at least initially along the coastal ports more from lack of funds to travel further inland. Mine came over in the 1790's from Dublin and accounts here referring to Irish immigrants that only or primarily spoke Gaelic don't ring a bell with me...it was already one of two or more languages needed in Ireland. You read of it far more with German immigrants here being non-English speaking and maintaining German newspapers, schools, books, etc. a generation or two after arriving.
You'd either need much earlier, substantial Gaelic-speaker immigration at the dawn of North American colonization and isolated enough in large enough communities to preserve it as their primary local language, so maybe along the Great Lakes, Carribbean islands, etc.. Being surrounded by English-speakers and more importantly it being the official language of most newspapers, magazines, education, public documents, trade and business, technology etc. as the 18th century became the 19th century, I think you'd still lose most of the Gael speaking dominance, albeit the French-speakers of Quebec or the displaced Acadians/Louisiana Cajuns, Indian tribes, etc. shows a not particularly handy language for local use can hang on far longer than expected.