The State Library of Pennsylvania’s digitized copies of historical Pennsylvania newspapers can be found in the AccessPA Digital Repository.
Currently you can browse issues of the following newspapers, among others:
In cooperation with Penn State and the National Endowment for the Humanities, the State Library of Pennsylvania also participated in the various Pennsylvania Newspaper projects that have been organized over the last several decades. The digital products of those projects can be found in the Chronicling America project.
Pennsylvania newspapers that have been digitized by other organizations can be found in the Directory of Digitized Pennsylvania Historical Newspapers (excel).