It is a repository for millions of historic items ranging across rare books, scholarly monographs, family chronicles, maps, press reports and varied ephemera, reaching back almost 300 years, and accessible on the society's website.

The holdings of the Balch Institute for Ethnic Studies were added in 2002, and those of the Genealogical Society of Pennsylvania in 2006.

The society has recently undertaken efforts to appeal to a younger demographic through its Young Friends programming.

[4] The society's building on the southwest corner of 13th and Locust Streets was formerly the site of the Patterson Mansion.

The mansion was demolished between 1905 and 1909 and the main block of a new fireproof building, again designed by Addison Hutton, was constructed on site.