books.google.com - Shows U.S. county boundary maps for the census decades superimposed on modern county boundaries. Gives background information on each census, including census availability for each county....http://books.google.com/books/about/Map_Guide_to_the_U_S_Federal_Censuses.html?id=pURb5FQ5EH4C&utm_source=gb-gplus-shareMap Guide to the U.S. Federal Censuses
