I caught an article on LancasterOnline (available here) that discusses a digitization project of the Historic Preservation Trust of Lancaster County. One of there somewhat monumental books about historic structures in the county has been made freely available to the public. Called Our present Past, it is organized by municipality and reasonably exhaustive. So if you got questions about historic structures, it probably has answers. You can access Our Present Past at http://opp.hptrust.org/nxtbooks/hptrust/presentpast/index.php.
Keith L Greenawalt, Reference Librarian/Public Services Manager