GWEN IFILL: Now: bringing health care to an often-forgotten population.

One out of three of those newly eligible for Medicaid under the Affordable Care Act are expected to be former inmates after their release from prison or jail. It's a story that hasn't gotten a lot of attention, but it represents a big change.

Sarah Varney of the Kaiser Health News collaborated with the NewsHour on this report.

SARAH VARNEY, Kaiser Health News: The Santa Rita Jail outside Oakland, California, is one of the largest detention facilities in the U.S. Some 3,000 inmates are currently housed here and many require medical treatment.

WOMAN: Hi, Jackson.

SARAH VARNEY: It costs the jail $28 million a year to provide medical and mental health services to the inmates. The pharmacy dispenses with 350,000 pills a month for conditions like depression, diabetes, high blood pressure, all common ailments among offenders, who tend to be sicker than the general population.

RICHARD LUCIA, Undersheriff, Alameda County, California: So, we have all of the medications that are required by doctor's prescription.

SARAH VARNEY: Richard Lucia is the undersheriff for Alameda County.

RICHARD LUCIA: We get a lot of sick people coming and physically ill people who come into our custody. We get them medicated and sort of stabilized. Once they leave our facility, there is no way to know what was going happen to them in terms of their medical care.

SARAH VARNEY: When inmates in California and around the country are released, most leave prison or jail with no health insurance and little access to medical care, but that's beginning to change.

The federal health care law encourages states to expand Medicaid to include all poor single adults, not just those who are disabled or who have children. Although Medicaid won't cover medical care for prisoners, except for longer hospital stays, public health experts say the change in the law represents an unprecedented opportunity for ex-offenders when they get out.

ALEX BRISCOE, Health Director, Alameda County, California: Historically, 10, 11 percent have been eligible for Medicaid. That number is well over 90 percent as of January 2.

SARAH VARNEY: Alex Briscoe is health director for Alameda County. He says enrolling men and women who have been incarcerated into Medicaid will save the county money and help former inmates.

ALEX BRISCOE: When they do need care, they come to our emergency department. They cost us between $600 and $800 a visit. So the cost drivers on our system are intense. We now have a chance to treat and reconnect communities to care and support.

SARAH VARNEY: The county is now making a big push to get men and women into Medicaid when they leave jail.

DONALD WILLIAMS, Healthy Oakland: Cone on. Let's roll.

SARAH VARNEY: Donald Williams is one of those on the front lines of the enrollment effort. A former inmate, Williams now works for a nonprofit called Healthy Oakland patrolling the city's neighborhoods for those who might be eligible.

DONALD WILLIAMS: We pick up three or four guys within a week, and sometimes I just get one. But it's basically all over — all over Oakland.

SARAH VARNEY: On the day we caught up with Williams, he was picking up three young men who were recently paroled, giving them a ride back to the Healthy Oakland clinic so they could do something they have never done before, apply for health insurance.

Twenty-five-year-old Rodrigo Salido spent two years in the maximum security wing at Santa Rita Jail. He was convicted of burglary, assault and gang involvement. While inside, he was diagnosed with bipolar disorder and prescribed an anti-psychotic drug.

MAN: Planning on staying out this time?

RODRIGO SALIDO: Definitely.

MAN: Good. Good.

RODRIGO SALIDO: I'm three strikes. I can't go back.

MAN: Oh, yes. No, you can't.

RODRIGO SALIDO: Everybody kind of told me like, dude, you got anger problems and you need to get some help. I started getting Risperdal. It's been helping me be more relaxed, you know, like not so much on the edge.

WOMAN: Mr. Salido, is there any medication that you are supposed to be taking today.

RODRIGO SALIDO: Just Risperdal.

WOMAN: OK. And the milligram bar?

RODRIGO SALIDO: Three.

SARAH VARNEY: Salido got out of jail in February and soon ran out of his medication. He's getting a preliminary checkup at Healthy Oakland, but once he gets his Medicaid card, he can regularly visit a primary care doctor, refill his meds and see specialists like a psychiatrist.

In fact, several studies have shown that ex-inmates who have access to health care when they leave jail, especially mental health and substance abuse counseling, are less likely to re-offend.

But not everyone supports extending Medicaid benefits to those who have done time. The subject recently during debate on the FOX News program "FOX & Friends."

MAN: So go to jail and get an insurance policy?

MAN: No, yes, go to jail and get Obamacare.

AVIK ROY, The Manhattan Institute: I think a lot of those people who work hard and play by the rules and are paying their taxes and paying their insurance bills say, hey, I was told that this was about helping people with preexisting conditions. I wasn't told that it was supposed to be about helping ex-convicts and people coming out of prison.

SARAH VARNEY: Avik Roy is a senior fellow at The Manhattan Institute, a conservative research group. While Roy agrees that access to health care reduces recidivism, he says access to Medicaid hasn't been shown to stop criminals from re-offending.

AVIK ROY: As much as we might intuitively think that this could be a way to address this problem, thus far, it hasn't been. The way that Medicaid has evolved over the last 50 years have made it very ineffective, because a lot of physicians don't accept Medicaid and don't see Medicaid patients. And, as a result, it's very difficult for Medicaid patients to get access to needed care.

SARAH VARNEY: Nineteen states, many led by Republican governors, have chosen not to expand Medicaid, over concerns about cost and federal overreach. Another five states are still debating their plans. That decision affects all poor single adults in those states, not just ex-inmates.

States that do expand, though, stand to receive a significant infusion of federal funds to cover all of those newly eligible. Efforts to target men and women who have been incarcerated are under way in Colorado, Oregon, Illinois, and elsewhere.

Here in Oakland, the county expects to enroll some 18,000 Medicaid-eligible inmates and detainees in the coming years, but even supporters like Alex Briscoe admit a Medicaid card is no panacea for troubled lives.

ALEX BRISCOE: You can't treat away the problems that face poor communities, right? It's about a good job. It's about a sense of meaning and belonging. It's about a place to sleep. So all of those basic human needs have to be met too. But health care can be a tool for social justice if it is delivered effectively and creatively. And that is why the Medicaid expansion is such a great opportunity for us.

SARAH VARNEY: Still, it may be some time before ex-inmates like Rodrigo Salido receive any benefits. California, like other states, has been overwhelmed by new Medicaid applications. And it's taking months for people to receive their benefits.

GWEN IFILL: Our partners at Kaiser Health News have more reporting on how the numbers of mentally ill behind bars have grown substantially. You can find that online.