For individual newspaper titles, check the CMU Library catalog for the most up-to-date access information. Other libraries may have copies of other newspapers. You can use either search Worldcat or the Center for Research Libraries' (CRL) catalog to see what might be available. CRL has more than 10,000 titles from most countries of the world and every state in the U.S., including over 1,800 U.S. ethnic titles and some of the earliest African American newspapers.
If you want to find names of historic American newspapers for a particular city, and the dates of publication, see: