The worst 31 counties — generally urban jurisdictions — have about a fifth of the country’s population but accounted for 42% of the country’s homicides in 2020, said John R. Lott Jr., president of the Crime Prevention Research Center, which conducted the study.

The worst 5% of counties accounted for 73% of homicides. That ticked up slightly from 69% in 2014 and 70% in 2016.

Meanwhile, 52% of counties recorded no homicides in 2020, and another 16% recorded only a single killing.

“Murders are a problem in a very small percentage of the counties in the United States,” Mr. Lott told The Washington Times.