Four states account for half of the nation’s wiretapping activity, according to a new report from the Administrative Office of U.S. Courts. Nevada leads the nation in the number of wiretaps when population is factored in, according to the annual list of where federal and state judges have authorized law enforcement to monitor phone communications as part of criminal investigations in 2013.

Wiretaps By StateThe report suggests that nearly 90% of the wiretap authorization requests cited criminal drug-related offenses; the rest ranged from smuggling to homicide cases. It found that the wiretaps led to 3,744 persons arrested (about the same as in 2012), and 709 persons convicted of a crime.

As Americans adopt cell phones over landlines, 97% of the total 3,576 authorizations specifically target portable devices including cell phones and digital pagers. Federal and state judges authorized a total of 3,455 wiretaps on portable devices in 2013. The total number of reported wiretaps is up 5% from 2012, but it’s more than doubled since a decade ago, when the number of wiretaps authorized was 1,442.

California, New York, Nevada and Florida lead the nation in the number of mobile wiretap authorizations. California dwarfs the rest of the nation with about 26% of the reported authorizations in 2013, more than doubling New York with 12%, and Nevada and Florida trailing with about 6% each. 

While these four states account for half of the nation’s domestic wiretaps last year, they together account for a quarter of the U.S. population. However, it may not surprise many that California, the nation’s most populous state, also reported the largest number of wiretaps of any state.

When we factor in population, Nevada leads the nation with 38 mobile wiretaps for every 500,000 people. Most Nevada wiretaps (187) were sought by officials in Clark County, home to Las Vegas; federal prosecutors in the state obtained authorization for 26 more, though only one was actually installed.

Why are there so many wiretaps in Nevada? We don’t really know: Law-enforcement officials in the state didn’t respond to our inquiries. The state does have the second-highest violent-crime rate in 2012, with 607.6 incidents per 100,000 people, according to the FBI’s Uniform Crime Reporting program. However, those figures may be skewed by Nevada’s fairly small resident population (2.8 million), the basis for the rate calculation, versus the millions of tourists who pass through each year.

After Nevada came Colorado and California (each with about 12 wiretap authorizations per 500,000 people) and New York with about 11 per 500,000. Only five states—Hawaii, Montana, North Dakota, South Dakota and Vermont— had no wiretap requests during 2013. (The District of Columbia had 17 authorzations per 500,000.)

While the report details wiretaps that move through the state and federal court system, published reports assert that other law enforcement and intelligence agencies — including the National Security Agency and Drug Enforcement Administration — share wiretaps and other information outside of the established court system.

Martin Shelton  is a former Data Analytics Intern at the Pew Research Center.