More than 11,000 gang members and their associates have been arrested over a three-year period thanks to a crackdown in immigration enforcement by the U.S. Immigration and Customs Enforcement.

(CNSNews.com) – U.S. taxpayers are spending at least $18.6 million per day to house an estimated 300,000 to 450,000 illegal immigrants who are incarcerated and eligible for deportation from the United States , according to data from the Department of Homeland Security (DHS) and the Department of Justice (DOJ).

The cost per day for these prisoners is based on Justice Department incarceration cost estimates from 2001 and on the lower-end figure of 300,000 incarcerated deportable aliens, which means the actual expense today could be substantially higher than $18.6 million per day.

The prisones involved here are foreign national who have come into the United States, committed a crime, been captured, and imprisoned.

Half of the undocumented aliens who were removed from the United States in fiscal 2010 (which ended on Sept. 30) had been convicted of a crime in the United States.

On Wednesday, the office of the DHS Inspector General (IG) released its annual performance plan report for fiscal year 2011, which states that there are “approximately 300,000 to 450,000 criminal aliens incarcerated in federal, state, county, and local correctional facilities [who] are eligible for removal from the United States.”

In its March 2010 report, "Immigration Enforcement Actions: 2009," the DHS defines removal as "the compulsory and confirmed movement of an inadmissible or deportable alien out of the United States based on an order of removal. An alien who is removed has administrative or criminal consequences placed on subsequent reentry owing to the fact of the removal."

Kara McCarthy, a spokeswoman at the DOJ, told CNSNews.com that the latest data available show that “average annual operating costs per state inmate for Fiscal Year 2001 was $22,650; in the Federal Bureau of Prisons it was $22,632.”

These annual operation costs exclude “capital expenditures, juvenile corrections, probation, parole, and most central office functions of corrections spending,” McCarthy told CNSNews.com

The cost of $22,650 per year to house just one inmate at the state level equals about $62 a day ($22,650 divided by 365 days). In the Federal Bureau of Prisons, it also averages out to $62 per day ($22,632 divided by 365 days).

Given this daily average expense (based on fiscal year 2001 costs), it can be estimated that the cost of housing 300,000 incarcerated illegal aliens in U.S. prisons would equal $18.6 million per day; the cost for housing 450,000 incarcerated illegal aliens would equal $27.9 million per day. If inflation in prison costs since 2001 were factored in, the expense would be even greater.

When CNSNews.com asked why incarcerated aliens who are eligible for removal have not been deported, a DHS spokesperson said, “It is because they are still serving their criminal sentence. ICE does not receive criminal aliens from state criminal justice systems until after they have completed their sentences.” (ICE is the acronym for Immigration and Customs Enforcement.)

On the same day the IG’s office released its performance plan report, DHS Secretary Janet Napolitano and ICE Director John Morton announced that half of the undocumented aliens who were removed from the United States in fiscal year 2010, which ended on Sept. 30, were convicted criminals.

“In fiscal year 2010, ICE set a record for overall removals of illegal aliens, with more than 392,000 removals nationwide,” says an Oct. 6 press release from the DHS. “Half of those removed--more than 195,000--were convicted criminals.”

“The fiscal year 2010 statistics represent increases of more than 23,000 removals overall and 81,000 criminal removals compared to fiscal year 2008--a more than 70 percent increase in removal of criminal aliens from the previous administration,” added the release.

Homesland Security Secretary Janet Napolitano.

It is uncertain whether the IG office’s estimate of 300,000 to 450,000 incarcerated criminal aliens who are eligible for removal takes into account the 195,000 criminal aliens removed in fiscal 2010. The IG office did not respond to CNSNews.com for a clarification on this point before this story was posted.

Nevertheless, the DHS did not deport all of the criminal illegal aliens who are eligible for removal and are currently sitting in U.S. correctional facilities.

The DOJ spokeswoman told CNSNews.com that, according to its latest figures, “In 2008 there were 785,556 inmates in the nation's [local and county] jails and 1,518,559 inmates in state and federal prisons.” That equals 2,304,115 inmates in total in the United States .

Given those numbers, 300,000 incarcerated criminal aliens would equal 13 percent of the entire inmate population of the United States, while 450,000 incarcerated criminal aliens would equal 19.5 percent of the entire inmate population.