National support for the death penalty is still in decline. A new Pew poll released last week found that 56 percent of Americans now support the death penalty, a decline of over 20 percent from its peak in 1996. Opposition to it rose to 38 percent. These numbers might still seem good for capital-punishment proponents, even considering the overall trend of decline, but they mask a deeper shift.

On paper, thirty-two states and the federal government currently allow capital punishment. But in practice, the death penalty has been largely abandoned throughout most of the United States. Juries now sentence fewer defendants to death than at any time since the Supreme Court lifted its de facto moratorium in 1976.

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Executions have also declined over the same time period, but for different reasons. A major factor is the recent shortage of lethal injection drugs across the country. Many states have also imposed moratoriums until the Supreme Court decides Glossip v. Gross, which could force changes in execution methods nationwide. Neither this nor the lengthy post-conviction appeals process would affect the rate of new death sentences.

Of course, death sentences and executions alike are statistically concentrated in a few states. This includes Alabama, Florida, Georgia, Louisiana, Oklahoma, Texas, and Virginia in the South, plus Ohio and Missouri in the Midwest and California and Arizona in the West. Even in these states that wield death sentences most frequently, numbers from the Bureau of Justice Statistics show a precipitous decline. Texas juries, for example, sentenced 48 people to death in 1999. In 2009, they only sentenced eight.

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Not only are death sentences declining overall and within the most execution-oriented states, the remaining sentences are largely concentrated in a few county-level enclaves. A 2012 study by DePaul University law professor Robert J. Smith examined death sentence and execution statistics in major death-penalty states, including Texas, Florida, Virginia, California, Oklahoma, Arizona, and others. By looking at cases over a five-year period from 2004 to 2009 on a county-by-county level, Smith found significant geographic disparities in the death penalty’s application.

Los Angeles County is only twice the size of [Illinois’s] Cook County, but Los Angeles County sentenced nearly five times as many people to death from 2004 to 2009. [Texas’s] Harris County has roughly one million fewer people than Cook County, but Harris County sentenced almost three times as many people to death. [Arizona’s] Maricopa County is roughly the same size as Harris County, but Maricopa County sentenced thirty-eight people to death while Harris County rendered twenty-one death sentences. [Florida’s] Miami-Dade County, which has a population of approximately 2.5 million, only sentenced four people to death, whereas Oklahoma County, which has a population of approximately 750,000, sentenced eighteen people to death.

The effect is even more dramatic in the aggregate. Of the 3,144 counties or their equivalents in the United States, just 29 counties averaged more than one death sentence a year. “That 1 percent of counties accounts for roughly 44 percent of all death sentences” since 1976, Smith observed. A 2013 report by the Death Penalty Information Center found that 59 counties—fewer than 2 percent of the total—handed down all U.S. death sentences in 2012.

As the map below shows, only a handful of counties handed down more than five death sentences between 2004 and 2009.

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Even fewer counties handed out more than 10 death sentences over the same six-year period.

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Part of this can be explained by population density: A rural Texas county with 5,000 people won’t have the same number of murders as an urban county with millions of inhabitants. But even among large cities within the same state, major disparities exist. Harris County, which includes the city of Houston, is responsible for more executions since 1976 than any state besides Texas. “Houston had 8 percent more murders than Dallas, but 324 percent more death row inmates; 15 percent more murders than San Antonio, but 430 percent more death row inmates,” the DPIC report found.

Why do these vast geographic disparities in capital cases occur, both between the states and within them? Those who bring the charges are one factor. The death penalty may be enacted by state legislatures, but county prosecutors impose it. Prosecutorial discretion is an unseen but elementary force that guides the criminal-justice system. Nowhere is that force’s impact better quantified than capital punishment. Longtime former Manhattan District Attorney Robert Morgenthau refused to pursue the death penalty in his jurisdiction after New York revived it in 1995, even for the killing of police officers. His counterpart in Philadelphia, Lynne Abraham, sought the death penalty in nearly every homicide case she prosecuted during the capital-punishment renaissance of the 1990s. In some Louisiana jurisdictions, Washington Post reporter Radley Balko described “a toxic culture of death and invincibility”:

[Exonerated death-row inmate John] Thompson was up against a prosecutorial climate that critics had long claimed valued convictions over all else, one that saw a death sentence as the profession’s brass ring. The New York Times reported in 2003 that prosecutors in Louisiana often threw parties after winning death sentences. They gave one another informal awards for murder convictions, including plaques with hypodermic needles bearing the names of the convicted. In Jefferson Parish, just outside of New Orleans, some wore neckties decorated with images of nooses or the Grim Reaper.

One of Thompson’s prosecutors, Orleans Parrish Assistant District Attorney James Williams, told the Los Angeles Times in 2007, “There was no thrill for me unless there was a chance for the death penalty.”

But even the most passionate district attorneys must bow to budgets. Capital cases are expensive and time-consuming. They require years of appeals, countless hours of testimony from experts and witnesses, and thousands of man-hours for both prosecutors and public defenders. These costs add up fast. Before Maryland abolished capital punishment in 2013, death-penalty prosecutions cost nearly three times as much as those seeking life sentences. A 2011 study found that California spent nearly $184 million a year on its vast capital-punishment system, but only executed 13 inmates since 1977. For smaller, rural counties with threadbare tax coffers, the increasing cost of the process often deters prosecutors from pursuing death sentences.

Americans may still be divided as to whether the death penalty is cruel, but there is no question that it is now unusual. Nominally, thirty-two states allow capital punishment. In reality, only a small fraction of counties are responsible for keeping the death penalty alive.