This is something that has been a long time coming. I've been saying for a million yerars that when you look at a crime map, you find that ALL the crime is done in a very small area.
In 2014, the most recent year that a county level breakdown is available, 54% of counties (with 11% of the population) have no murders. 69% of counties have no more than one murder, and about 20% of the population. These counties account for only 4% of all murders in the country.
The worst 1% of counties have 19% of the population and 37% of the murders. The worst 5% of counties contain 47% of the population and account for 68% of murders. As shown in figure 2, over half of murders occurred in only 2% of counties.
Murders actually used to be even more concentrated. From 1977 to 2000, on average 73 percent of counties in any give year had zero murders. Possibly, this change is a result of the opioid epidemic's spread to more rural areas. But that question is beyond the scope of this study. Lott's book "More Guns, Less Crime" showed how dramatically counties within states vary dramatically with respect to murder and other violent crime rates.