SAN DIEGO — At least 140 people have died in San Diego County jails since 2009, the year Bill Gore took over as sheriff. That’s an average higher than one inmate a month, every month, over the last 10 years.

Some died by natural causes — chronic health conditions such as heart disease and diabetes are often found in people who end up in jail. Others are slain or overdose on drugs.

Dozens have taken their own lives, though Gore and his top command staff say they do everything they can to identify suicidal inmates and treat mental illness.

“The Sheriff’s Department is committed to keeping inmates safe and is continuously looking for best practices in the delivery of mental health care,” the department said in a video posted on its website in May.

A six-month investigation by the San Diego Union-Tribune shows that the county’s jail mortality rate is the highest among California’s largest county jail systems. The grim history shows no sign of waning.

Fifteen inmates died in county custody in each of the last two years, out of a population of more than 5,000. Twelve inmates have died so far this year.

Over the last several years, the department has improved training, changed healthcare providers and brought in new equipment. But it has been slow to make more obvious fixes, such as installing fencing to prevent suicidal inmates from jumping, or bolstering its mental health staff to provide around-the-clock care.

The loss of life causes more than anguish for friends and relatives of those who perish. The deaths cost taxpayers millions of dollars in legal settlements and attorney fees.

Over the last decade, the county paid at least $7.9 million to families of people who died or were badly injured in jail. That’s more than four times the $1.9 million cost of similar legal actions in the prior decade, before Gore was appointed sheriff.

The total does not include a $12-million jury verdict awarded in July to a North County man who suffered brain damage from a fall after being arrested and booked into jail.

San Diego County is defending itself in at least a dozen other state and federal lawsuits brought by inmates and family members. Some recent deaths also are probably headed to court.

The continuing deaths and lawsuits are reflective of the county’s indifference, critics say.

“A measure of society is how we treat our most vulnerable. By that measure, San Diego County is failing miserably,” said Julia Yoo, a San Diego attorney who has sued the sheriff repeatedly on behalf of deceased inmates’ families.

According to Sheriff’s Department reports, 140 people have died in the county’s seven detention facilities since 2009, the year Gore was promoted from undersheriff by the Board of Supervisors after the midterm resignation of William Kolender.

One inmate killed himself July 3, 2009, Gore’s first official day in charge.

The rise in jail suicides was even more pronounced. From 1999 to 2008, 23 inmates killed themselves, the Sheriff’s Department said. The number of suicides from 2009 to 2018 increased to 39, a 70% increase.

San Diego County’s overall mortality rate over the last decade is the highest among California’s six largest jail systems, according to data those departments are required to report to the state Department of Justice.

The county recorded an average of 12.8 deaths a year, for an annual mortality rate of 246 per 100,000 inmates.

By comparison, Los Angeles County, whose jail system is three times larger than San Diego County’s, had an inmate mortality rate of 158 per 100,000 inmates. San Bernardino County’s was 149, and Sacramento County’s was 94.

The most prominent reported reason for jail deaths is natural causes.

Of the 140 deaths in San Diego County jails since 2009, nearly half were attributed to natural causes. Autopsy reports suggest some of those deaths might have been prevented if inmates had received better medical care. Reports show multiple inmates dying from treatable conditions such as diabetes, pneumonia and stomach ulcers.

The second most common cause of death was suicide. San Diego County’s jail suicide rate is higher than that of the other five large counties, at 75 per 100,000 over 10 years.

In Los Angeles County, the rate was 26 per 100,000. The rates in San Bernardino and Sacramento counties were 44 and 23, respectively, and Orange County reported the lowest at 15.

The Sheriff’s Department argues that the demographics of local jail populations account for the differences in suicide rates across the state. Either way, the stories of jail suicide are harrowing examples of an undeniable mental health crisis within the criminal justice system.

At least 17 inmates have died from drug overdoses since 2009. Seven were able to obtain a lethal amount of drugs in jail, autopsy records show. The others ingested drugs before their arrest.

Gore has said publicly that stopping the smuggling of drugs into jails presents a continuing challenge.

“You can’t imagine the ingenuity of inmates,” the sheriff told the Citizens’ Law Enforcement Review Board at an April meeting of the oversight panel.

A smaller but growing number of inmates in San Diego County jails have become homicide victims. The Sheriff’s Department reported 10 in-custody homicides since 2009, a fivefold increase over the prior decade.

Most of the victims were attacked by other inmates.

Over the years, the Sheriff’s Department introduced tools and procedural changes aimed at reducing jail deaths.

In early 2015, for example, following 11 suicides in less than two years, the department developed a suicide-prevention program.

Officials strengthened intake screening so booking staff would ask more pointed questions of arresting officers and of inmates. The idea was to ensure detainees were housed in appropriate settings and steered into treatment.

The department also launched a video-based “telepsychiatry” program, so inmates could speak to a doctor more often. That program ended because of data-security concerns.

The jail also created “enhanced observation housing,” so deputies could better monitor inmates who express an intent to harm themselves. Inmates in these units are given tear-proof smocks and blankets and sleep on mats or bunks that have been modified to reduce the chance that an inmate hangs themselves.

Success has been elusive.

By the end of 2015, six more inmates had killed themselves. In 2016, five inmates died by suicide, and at least half a dozen have taken their lives since 2017.

McDonald, Davis and Schroeder write for the San Diego Union-Tribune.