The Trump administration's zero tolerance policy for illegal immigration is shining a spotlight on U.S. detention efforts. Recent government handout images show children lying on the ground with Mylar blankets in kennel-like wire cages. Audio obtained by ProPublica captures children crying after being separated from their migrant parents.

Kyle Walsh | CNBC

Though Trump signed an order he says will keep migrant families together, the detention facilities drawing the most attention right now aren't the only ones in the U.S. As of this month, U.S. Immigration and Customs Enforcement runs 113 detention facilities across the country and works with state and local jails along with private prisons to operate hundreds more.

ICE facilities cost $133.99 a day per adult

According to ICE's FY 2018 budget, on average it costs $133.99 a day to maintain one adult detention bed. But immigration groups have pegged the number closer to $200 a day. The cost to maintain a family bed, which keeps mothers and children together in a family residential center, costs around $319 a day, according to DHS. But as of April, children have been separated from their parents with much higher frequency, which has led to the creation of "tent cities" to hold thousands of separated children. Those beds cost $775 per person per night, HHS told NBC News.

Migrant children, many of whom have been separated from their parents under the "zero tolerance" policy by the Trump administration, are being housed in tents next to the Mexican border in Tornillo, Texas, U.S. June 18, 2018. Mike Blake | Reuters

An ICE spokesman said it does not detain unaccompanied children. However, it does oversee "juvenile facilities," managed by local jurisdictions, that allow for "temporary housing of children separate from adults." The average bed rate for this type of facility is $139.40 per day, according to ICE. However, ICE estimates often lack in transparency and don't reflect the true cost. There's been so much discrepancy that the U.S. Government Accountability Office looked into ICE's budget requests and found that its methodology was inaccurate and recommended a change in the way it comes up with its cost estimates. And then there's the question of how long immigrants are detained. ICE estimates an average stay of 44 days, but thousands of immigrants have been held far longer. In one case heard by the Supreme Court, an immigrant spend three years in detention. The DHS projects there will be an average of 51,379 people held in immigration detention centers each day in fiscal 2018, a sizable jump from the last few years, which have hovered near the low 30,000s. The increase stems follow's President Donald Trump's hardline policy against illegal immigration.

The executive order

On Jan. 26, 2017, Trump announced an executive order called "Enhancing Public Safety in the Interior of the United States." It broadened the scope of who is at risk for deportation, called for thousands of new ICE agents and directed DHS to use state and local police more to help enforce immigration law.

ICE officers in search of a man question his mother about his whereabouts in a morning raid on his r Irfan Khan | Los Angeles Times | Getty Images

A number of ICE's official reports reference Trump's executive order as a reason for ramping up operations. And that means more taxpayer money will be funneled toward immigration enforcement and deportation. But that doesn't mean people aren't profiting. In fact, private prison companies are making lots of money off detaining immigrants.

Private profits

Private prisons get stipends from the government to take over responsibilities of running a prison. To get that stipend, their costs must be lower than that of a public prison. The more beds a private prison can fill, the more funding they'll get from the government. And just like any business, the more costs they can cut, the bigger that profit margin will be. But many times, that results in poor quality of care for prisoners.

A guard escorts migrant detainee from his segregation cell back into the general population at the Adelanto Detention Facility in Adelanto, California. The facility is managed by the private GEO Group. Getty Images

Just look at GEO Group, one of the country's largest private prison corporations. It donated hundreds of thousands of dollars to a Trump-aligned super PAC, hosted its annual leadership conference at one of Trump's golf resorts, and just after Trump's election — its stock soared. Its shares have gained more than 8 percent this year. In ICE's FY 2018 budget, it says a "Longer Average Length of Stay (ALOS) will also drive the need for additional detention beds." Now, GEO Group officials say they expect earnings to rise with increased immigration detention time. ICE budget requests have skyrocketed under Trump. Even as the president vowed to stop separating families at the border, his zero tolerance policy is still in effect.

WATCH: Trump signs order that he says will keep migrant families together