The search for nineteenth-century naturalization records can be one of the more frustrating aspects of genealogical research. Before September 27, 1906, naturalization was carried out by thousands of courts—federal, state, county, local—and each court kept its own records. Where does one begin to look?
Researchers tracking down people who were naturalized in New England have an advantage, though. The National Archives–Northeast Region (Boston) has a unique set of records that brings together naturalization documents created in various New England courts. These records consist of photostatic copies, called "dexigraphs," made in the 1930s, of naturalization proceedings in all courts—federal, state, county, and local—in five of the New England states (Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont) between 1790 and September 26, 1906.
You can read the remainder of this excellent article by Walter V. Hickey at: http://www.ilw.com/lawyers/articles/2005,0603-hickey.shtm