US Immigration Finding the Place of Origin
Records that generally provide the country of origin include the U.S. censuses beginning in 1850, biographies, death records, obituaries, naturalization declarations or petitions, pre-1883 passenger lists, and military records. These records do not usually list the exact town that the ancestor came from.
Before you can effectively search the records of another country, you need to know the name of the city or town your immigrant ancestor came from. Clues about an ancestors' town of origin are found in various sources, including diaries and other records in your family's possession. You may find the town of origin in family and local histories, church records, obituaries, marriage records, death records, tombstones, passports (particularly since the 1860s), passenger lists (particularly those after 1883), and applications for naturalization.
The New York Times has published an interactive map, "Immigration Explorer," that gives summary place-of-origin information for each county in the United States for each decade from 1880 to 2000. Since people often immigrated in groups, seeing the predominant groups in the counties your ancestors settled in can provide clues regarding their origins. See http://www.nytimes.com/interactive/2009/03/10/us/20090310-immigration-explorer.html