U.S. life expectancy varies by more than 20 years from county to county
Not only county-to-county.  My friend did his PhD dissertation on how (at least in Rochester, NY), life expectancy varies by decades between zip codes.  His research focused on urban Food Deserts and studied how the lack of access to healthy food nearby restricted diets to that available in convenience stores (chips, soda, etc).  I wish I had access to his dissertation, but he just defended a month ago and cannot find it in any publications right now.EDIT:  Not my friend's paper, but here is a similar study: https://hrs.isr.umich.edu/publications/biblio/8355