• A German surname ending with -li almost always comes from Switzerland, or at least southern Germany.
• The ending -ski is often from Polish areas.
• Patronymic endings such as -son or -sen suggest Scandinavian areas, or if German, the province of Schleswig-Holstein.
• German families with French given names may be from areas such as Alsace-Lorrain, on the French side of the Rhein River.
• Prefixes such as Mc- and O’ in Scottish and Irish surnames suggest a specific clan, which usually had an ancestral area within their respective countries, although the immigrant may not have been raised in that area.

This approach can be quite complex, and usually requires the assistance of persons well versed in the language and culture of your immigrant family. Sometimes talking the subject over with a local university or college language department will help.