NEARLY 20 years ago, I was a social worker in a county jail where I first began to understand just how frequently the police deal with people with mental illnesses. Run-ins with the police were a regular occurrence for many of my clients, with officers often knowing them by name. They were overwhelmingly poor, and poor people with mental illnesses are also likely to experience homelessness and substance abuse — issues that place them at increased risk of police contact and incarceration.

All too often, those interactions can end in violence and death, as was the case with 19-year-old Quintonio LeGrier, who was shot and killed by a Chicago police officer last month. Responding to a 911 call made by Mr. LeGrier’s father, officers found Mr. LeGrier wielding a baseball bat, and one officer quickly opened fire.

This was not Mr. LeGrier’s first encounter with law enforcement. He’d had several confrontations with the police at the university he’d attended in recent months — at least one of these incidents involved officers’ guns being drawn. His experience bears a striking resemblance to that of one of my former clients who was a college student in the late 1990s and who had several tense exchanges with the police as his symptoms worsened.

What’s remarkable is that, even about 20 years later, the police remain the primary responders to mental health crises like these. According to data compiled by The Washington Post, of nearly 1,000 people shot and killed by police officers in the United States in 2015, 25 percent displayed signs of mental illness. And about 14 percent of individuals in American jails and prisons have a serious mental illness, which means that, for most officers, interacting with individuals with mental illness is an almost daily occurrence.