I recently did a webinar about using Chronicling America to its fullest and obtaining more ancestor articles. In so doing, it was an interesting comparison of the number of online newspapers on that site versus the number of newspapers ever published in America.
What is your guess of the percentage? 10%? 20%? 5%?
No, the answer (at least with respect to Chronicling America) is that there are approximately 2,000 online titles and there have been over 150,000 titles ever published in the U.S. That yields just a tad over 1%.
Of course, Chronicling America doesn't represent all of the online titles and images available. My research results in about 13,500 free online links for the U.S. (see the Newspapers! Page on this website for all the links). So 13,500 (online) in comparison to 150,000 (published) - and even if you account for some of the paid sites, such as GenealogyBank, Newspaper.com, etc. would likely yield just about 15-20%.
That leaves about 80-85% that ARE NOT ONLINE! Now what the heck do we do? The Library of Congress helps us out with the US Newspaper Directory from 1690 - Present so we can do offline research.
This directory provides not just multiple ways to find newspapers published, but tons of facts about those newspapers. Just do your choice of searches from the main US Newspaper Directory from 1690 - Present page. Here's an example of a "fact" page".
From this "facts" page, you can actually find out where the newspaper is held. Just click on the "View complete holdings information" link at the bottom. Here are some examples for this newspaper:
Don't give up if your paper of interest is not online. Visit the US Newspaper Directory from 1690 - Present from the Library of Congress.
And if you are a "visual" learner, go to this tutorial. It is only a minute long - you can spare a minute! This will show you the very few steps as written above to find where your desired newspapers are available.
Good luck - persistence will win out.