BRIDGEWATER — The Massachusetts prison for men with a mental illness has long been known as a rough place where guards often strapped patients down or locked them in isolation cells for misbehavior — and where some patients met gruesome deaths.

It was an appalling, often inhumane place, an embarrassment to the state that seemed — to the mentally ill and their advocates — like it would never change.

But it has. In April, a private firm hired by the Baker administration replaced almost all the guards at Bridgewater State Hospital with a specially trained security force, along with psychiatrists and other clinicians equipped to provide more humane methods of handling distressed patients. Governor Charlie Baker called it “a culture change.’’

Five months in, the results are remarkable, beyond the imagining of mental health advocates. Since Correct Care Recovery Solutions took over management of the facility, the staff has cut the seclusion of patients by 99 percent and the practice of strapping them down by their wrists and ankles by 98 percent.

“I didn’t think they’d be able to make the changes they’ve made, but they have the right philosophy and what they’ve done in five months is astounding,’’ said Christine Griffin, executive director of the Disability Law Center, which has been monitoring conditions at Bridgewater under the settlement of a lawsuit filed on behalf of patients and their families.

“It’s all very impressive. I give them credit,’’ added James Pingeon, an attorney with Prisoners’ Legal Services who has spent decades pushing for more humane treatment at Bridgewater. “The atmosphere is palpably different down there.’’

It’s a far cry from just a few years ago, when Bridgewater was by far the harshest mental health facility in Massachusetts, employing seclusion and restraints to control patients at more than 100 times the rate of staff at facilities run by the Department of Mental Health. The 2009 death of 23-year-old Joshua Messier, who suffered a heart attack as Bridgewater guards wrestled him into four-point restraints, sparked calls for reform when the Globe revealed in 2014 that state officials had covered up the circumstances surrounding his death.

On Thursday, a Globe reporter and a photographer toured the facility and witnessed the changes firsthand. Bridgewater has been made to look and operate more like a hospital, and less like the state prison it still is.

The nearly 200 men consigned to Bridgewater, mostly for psychiatric evaluations after being charged with committing crimes, wear street clothes, not prison garb. Some of the mental health workers wear hospital scrubs, a striking contrast to the uniformed guards of old. And flowers, along with other amenities, including a gazebo, have been added to the main yard.

Meanwhile, dormitories are being renovated so that each patient has his own room, most of them painted green or other earth tones. Many are encouraged to take part in group activities, such as gardening and singing.

The changes are more than cosmetic. The notorious Intensive Treatment Unit, where men were routinely strapped down to their beds or held in isolation — and where Messier died — has been closed. The same is true of “the bird cage,’’ a narrow cell where patients from the ITU were sometimes held in shackles while they talked with their lawyers.

In addition, Correct Care has replaced about 50 low-quality video cameras with nearly 450 high-resolution cameras to better monitor both patients and their treatment, and to ensure the safety of clinicians. The company has also introduced electronic recordkeeping to supplant reams of paper forms that were often illegible to supervisors or outside evaluators.

Perhaps most significant, hospital administrators are instilling in the staff a new commitment to treat the men at Bridgewater like people afflicted by illness rather than dangerous convicts, referring to each one as a “person served.’’

During the tour, hospital administrator George Gintoli and assistant administrator Kevin Ann Huckshorn were on a first-name basis with many patients, who freely mingled with the Globe staffers.

“This is really a passion,’’ said Gintoli, a veteran of other facilities similar to Bridgewater, known as forensic hospitals.

He acknowledged that some of the clinicians held over from the previous administration are uncomfortable with the new model and say they would feel safer if the guards returned. Still, Gintoli said that violent incidents against clinicians have not increased since the guards were replaced. Easing the risk to staff, about 40 Bridgewater patients who had been convicted of crimes were transferred to two mental health units at Old Colony Correctional Center when Correct Care took over.

Huckshorn, a nationally recognized expert in reducing the use of seclusion and restraints in mental health care, is practicing what she has often preached. Three years ago, in a Globe interview about Bridgewater, she said efforts to reduce the use of seclusion and restraints at any facility were doomed to fail unless top administrators were directly involved.

“If the senior leadership is not fully engaged from the very beginning and have a commitment to be fully engaged for a number of years, it won’t work,’’ she said at the time.

Baker, in an interview Friday, said he made reforms a Bridgewater a top priority — unveiling his plans in his state of the state address earlier this year — because he had heard firsthand accounts of patients who had been mistreated and had read internal investigative reports and news stories about the facility.

“This is long overdue. It’s something that’s troubled me for a while,’’ he said, adding that credit for the changes also belongs to the Legislature, which approved a 39 percent increase in Bridgewater funding, an additional $19 million, as well as the union representing the guards, which supported the staffing changes. “We’re very pleased by the early progress here on every level,’’ he said.

Correct Care Recovery Solutions is a division of Correct Care Solutions, a Nashville-based firm founded by someone with intimate knowledge of Bridgewater State Hospital. Executive board chairman Gerard Boyle served as the hospital’s superintendent and as associate commissioner of the Department of Correction during the late 1980s and early 1990s.

But Bridgewater took a dark turn in the years after Boyle departed. After Messier’s 2009 death, two other men died at Bridgewater after being strapped down to their beds, one in 2010 and another in 2013. And after the Globe revealed the Department of Correction’s attempt to conceal the violent nature of Messier’s death, a special prosecutor appointed by the attorney general secured manslaughter indictments against three of the guards who were in his cell the night he died. The guards could stand trial later this year.

Lisa Brown, Messier’s mother, said that her son would be pleased by the changes at Bridgewater, and she praised Baker for following up on a promise to introduce more humane treatment methods at the facility.

“The changes mean a lot to me, but they would have meant so much more to Joshua,’’ she said. “I’m really grateful to Governor Baker for following through. He’s given me more faith in humanity and in government than I’ve had in a long time.’’

After Messier was killed, attorney Roderick MacLeish Jr. filed a lawsuit on behalf of Bridgewater patients and their families, alleging that guards at the facility were routinely using seclusion and restraints illegally. The suit was one of many he has filed regarding conditions at Bridgewater dating to the early 1980s.

“I think of all the people who suffered there and died there, but after 35 years of litigating. this is really good to hear,’’ he said. “What’s happening at Bridgewater is really extraordinary.’’

Still, many advocates fear that conditions will eventually deteriorate at Bridgewater unless the facility is taken away from the Department of Correction and transferred to the Department of Mental Health.

“Bridgewater is still immune from all the laws and regulations that the Department of Mental Health has to abide by,’’ said Pingeon, the attorney with Prisoner’s Legal Services. “Bridgewater could slide backwards in a hurry.’’

Baker told the Globe he would be open to discussing transferring the facility to the Department of Mental Health, but would be reluctant to do so if the new model of care is successful.

“I’m open to having that conversation, but if the thing is working under the current construct, I would hesitate to change that,’’ he said.

Baker also said he is committed to improving services for mental health patients living outside the criminal justice system. Recent upgrades, he said, include increasing insurance reimbursement rates for mental health care under MassHealth and hiring 50 additional adult case managers at the Department of Mental health to supervise adults with mental illness living in community settings.

The failings of the state mental health care system were the subject of a series of Globe Spotlight Team stories last year.

Nothing has highlighted the neglect of people with a serious mental illness like the barbaric conditions that have often prevailed at Bridgewater in recent decades.

But now, consider this: On Thursday, a small group of patients was meeting with a music therapist in the newly constructed gazebo in the main yard. The therapist was playing a guitar, trying to lead the men around her in a rendition of the Bob Dylan anthem, “The Times They Are A-Changin.’’

Michael Rezendes can be reached at michael.rezendes @globe.com. Follow him on Twitter @MikeRezendes.