The Unpopulated United States

When we go up to Rhinebeck, NY for the Sheep and Wool Festival, we usually take US15 to Harrisburg and either I-78 or I-81/84 to I-87.  Either way, but particularly the latter, leads through sparsely populated areas, but even the more populated areas don't seem particularly densely settled.  

According to this site some of the counties have less than 100 people per square mile.  Reminds me of James Carville's crack about Pennsylvania being Philadelphia and Pittsburgh with Alabama in between. 

You can guess that all those sparsely settled counties vote Republican, then and now.