It isn't population density, it's crowded enclosed spaces and the people who can't or won't avoid them.
As the world’s attention was fixated on the horrors in Italy and New York City, the per capita death rates in counties in the impoverished southwest corner of Georgia climbed to among the worst in the country. The devastation here is a cautionary tale of what happens when the virus seeps into communities that have for generations remained on the losing end of the nation’s most intractable inequalities: these counties are rural, mostly African American and poor.