In addition to the above great links, I might add this one from German (in Englisch, but mostly linking to German sites

):
genealogy.net
Quote:most of the germans came from south-southwest germany
According to a PDF-publication by the Rhineland Regional Museum Kommern (in German:
http://www.migration.lvr.de/Aktion&Angebote/Schulaktionen/Museum-Kommern%2072%20DPI.pdf)) until ~1840 most German immigrants came from the alemanic-palentine-bavarian region.
From mid-1840's onwards, West Germany became an immigrant region as well: until the turn of the century, 15% of German immigrants came from the Rhineland and Westphalia.
Zunkel* calculates that about 290,000 persons from the Rhine Province immigrated to the USA, mostly from the districts of Coblenz and Trier. (*Zunkel, Friedrich in: Auswanderung als notwendiges Ventil: Gesellschaft-wirtschaftliche Verhältnisse in den rheinischen Territorien und ihre Auswirkungen auf die Auswanderung im Zeitalter des Absolutismus und der Frühindustrialisierung, n.d.; [obviously unpublished] lecture, made on May 15, 2000, at Brauweiler Abbey, Puhlheim, at the scientific symposium "Nice new world - immigration from the Rhineland to America from the 17th until the 19th century" ['Schoene neue Welt - Auswanderung aus dem Rheinland in die USA vom 17. bis zum 19. Jahrhundert '])