I have done quite a bit of Gately research in USA and Ireland - just across the Roscommon border in County Galway. Ancestor was Patrick Gately (~1816-1908) married to Barrett (d. 1901). Many of their children & grandchildren emigrated to the USA, UK, and other places.
I was lucky enough that my living great aunt (Delia Gately Carty) had remained behind on the family farm in far west of County Galway near Ballinlass and thus I had a well established locale for researching Irish records.
But tracking down the immigrants to the USA has not been so easy! Some settled in St. Louis and Cincinnati. Family lore has it that several aunts married Doyle, Finn, Cox, and McGuire. Some other related surnames from Ireland and worldwide are O'Halloran, Halloran, Anglin, Crehan, Arnold, Ramsey, Lynam, and Carty. Some probable related surnames are from the local area in Ireland are Mannion, Fallon, Rogerson,, Lenan, Verdon, Kelly, Geraghty, Glynn, Cox, Kenny, and Martin.