An important genealogical and historical resource can be books. Now with all the access we have to digitized books through services like Google Books and Heritage Quest, it has become easier to track down books about our ancestors and where they lived.
When using a book, don't forget to check out the footnotes and the bibliography. These two very important resources provide you with clues where you can search further. The author has already done quite a bit of research and they put that information in the bibliography and the footnotes/endnotes. Use that to further your own research. Find which books and articles might help your research from the author's list and then look for them at your local library or through interlibrary loan.