Philadelphia: A Brief History
Philadelphia: Finding the Hidden City
Metropolitan Philadelphia: Living with the Presence of the Past
There are many other excellent research libraries in the Philadelphia area that may be of interest.
Visit their websites first to determine which collections are available online, which collections are only available in-person, and how to best plan your visit.
Need additional help with using archives? The Society of American Archivists (SAA) has a useful guide to conducting archival research, called Using Archives: A Guide to Effective Research.
