In Philadelphia county, 602 people were in jail for every 100,000 in 2006, according to "Jailing Communities: The Impact of Jail Expansion and Effective Public Safety," a study by the institute, a Washington, D.C., criminal-justice think tank. That's up from 369 per 100,000 in 1996, the study says.

Two Tennessee counties followed Philadelphia: Davidson (includes Nashville), with 596 per 100,000, and Shelby (includes Memphis), with 594.

Rising jail populations have resulted in huge bills for local municipalities across the country.

More than $19 billion was spent on jails nationally in 2004.

"I do think that since the 1970s we've definitely had an increased desire to punish," said study co-author Amanda Petteruti.

The study looks specifically at the number detained in jails, locally run facilities that traditionally hold people with short sentences or people awaiting trial who were either denied bail or could not post it. Prisons are typically reserved for longer sentences.

Petteruti said that a variety of factors contributed to the jail population jump - rising bail costs and more people being detained on minor infractions, more being held pretrial or sent to county facilities due to overcrowded prisons.

"The purpose of jails have changed," she said. "Jails were used to hold people that may have been a flight risk . . . or [needed] to serve county time."

One reason that the report gives for more jail inmates is the rise in "broken windows" policing, which cracks down on smaller infractions and quality-of-life crimes to try to lower overall crime rates.

But Petteruti said that this technique can clog jails.

"For example, we know that in Los Angeles the chief of police has instituted this policy, they've increased the number of cops on skid row," she said.

"They're issuing tickets for infractions like jaywalking. The people can't pay and then they go to jail."

Philadelphia recently launched an aggressive crime plan, putting more cops on the street to drive down crime rates.

The report says that communities should offer more pretrial release programs, incarceration alternatives such as day-reporting programs and reduced sentences for nonviolent crimes.

Petteruti said that people can maintain a job, see their family and stay in better health outside the jail system.

"You're far more likely to contract anything from AIDS to staph infections [in jail]," she said.

City Finance Director Rob Dubow said that prison costs - which include jails - are one of the city's fastest growing expenses. The prisons budget for the current fiscal year is $218 million.

Dubow noted that Philadelphia gets little aid from the state or federal government for prisons. And he said that other cities share prison expenses with the county government - but that Philadelphia city government also oversees the county.

"Since we are the county, we bear all those costs," Dubow said.*