WHAT forces compelled so many in postfamine Ireland to resettle in North America? With an emigration rate more than double that of any other European country, Ireland in this period has received considerable scholarly attention. (1) Yet most studies focus on larger structural forces--chiefly capitalist transformation of agriculture from tillage to pasture--to neglect of local conditions and role of specific migration links between Ireland and America. Allied to this, Irish-American community studies seldom determine where precisely in Ireland their subjects originated or what, beyond larger structural forces, compelled them to emigrate. While not centered on study of Irish migration, David Emmons' award-winning Butte Irish: Class and Ethnicity in an American Mining Town, 1875-1925 asked important question: Where specifically in Ireland were Irish in his story from? Emmons concluded that the Irish-born among Butte's thousands of Irishmen were principally drawn from idle copper mines of Cork and from landless farm laborers and small farmers of of Ireland. (2) He based his conclusion on place-name association, noting that six most common Irish surnames in Butte closely associated with Co. Cork. (3) To support his place-name association evidence, he also cited Riobard O'Dwyer's genealogical studies of Beara Peninsula, a copper-mining district in Cork, which confirmed considerable migration to Butte. (4) In a more recent work Emmons returned to Cork-Butte nexus and again concluded that concentration of Corkonians in Butte was historical accident, citing as further evidence that West Cork had had only copper mines in Ireland, at Hungry Hill, near Allihies. (5) What Emmons did not realize is that nineteenth-century Ireland contained several copper-mining districts, two of which (Knockmahon in Waterford and Avoca in Wicklow) equaled or exceeded Allihies in both production and number of workers engaged. (6) While Emmons and O'Dwyer demonstrated a strong migration link between Beara Peninsula and Butte, existence of additional Irish copper districts raises important questions. Did other mining districts send such numbers to Butte? If not, why? Moreover, while Emmons asserted that County Cork in southwestern Ireland supplied a hugely disproportionate share of Butte's population, (7) it must be remembered that Cork was Ireland's largest county and produced by far greatest number of emigrants in this era. (8) It is therefore reasonable to assume that Cork surnames predominated in many other Irish-American communities. This essay will also explore that supposition. Emmons' scholarship has made an indispensable contribution to our understanding of Irish in America. His discovery of chain migration between copper districts in Cork and Butte invites further investigation into migration patterns of nineteenth-century Irish copper miners. This essay endeavors to offer such an investigation. Its objectives are fourfold: first, to present a brief narrative on Irish copper mining and role of Irish copper miners in development of two primary nineteenth-century American copper ranges, Michigan's Keweenaw Peninsula and Butte, Montana; second, to offer a more precise method of determining surname frequency in Ireland; third, to apply this refined method to Beara Peninsula and two other major Irish copper-mining districts, Knockmahon and Avoca; and, finally, to correlate surname frequency of three primary Irish copper-mining districts to surname frequency of both Butte and Keweenaw Peninsula. To determine surname frequency in Ireland, this study will utilize indexes to Griffith's Valuation, (9) which, owing to shortage of other complete Irish records, often serves as a substitute census. (10) Taken between 1848 and 1864, survey lists all householders and lessees by parish, no matter how small, and occupant and value of each separate piece of property. …