To find the newspaper you want, click on the first letter of the alphabet for the state in which it was published.
Example: To find the Toledo Blade, click on the "O" for Ohio.
The Library of Congress's web site, Chronicling America has a search engine that will identify United States newspapers that were available in a particular place and time. Click on this link to connect to the Newspaper Directory.
The Boston Public Library has digitized a number of newspaper directories for various years. If you're trying to identify what newspapers were published in a particular place at a particular time, you can view these directories.
If dates of coverage are included in an entry for a newspaper, the source may or may not include all issues within the listed time period. Also, the dates of coverage were correct when they were added to the entry, but may have changed since they were recorded.
The Google News search box searches back to 1970. It is available at: http://news.google.com/news/advanced_news_search
In order to search the newspapers in Google News Archive, do a search in a Google search box that includes the term(s) for which you wish to search and include the phrase "site:news.google.com/newspapers" (without the quotation marks) in the search box. For example, to search for articles about Pearl Harbor, do the search:
site:news.google.com/newspapers "pearl harbor"
A complete list of newspapers available at Google News Archive is at: http://news.google.com/newspapers That list is arranged by title of the newspaper and provides access to a browsable list of all issues available.