Data from the US Substance Abuse and Mental Health Agency (SAMHSA) suggests 20 percent of American adults -- 44.5 million people -- experienced some sort of mental illness over the last year.

The report defines "mental illness" as any sort of diagnosable mental, behavioral or emotional disorder that causes "substantial functional impairment" or requires treatment, and provides a list of how much of each state's population has suffered such a disorder.

“Mental illnesses are treatable and people can recover to live full, productive lives," SAMHSA Administrator Pamela S. Hyde said in a statement. "Unfortunately in the past year only 37.9 percent of adults with mental health problems received any type of care.”

According to the SAMHSA report, the states with the most occurrences of adult mental illness are:

1. Rhode Island (24.2 percent)
2. Utah (24.1 percent)
3. Idaho (22.5 percent)
4. Indiana and West Virginia (22.0 percent)

States with the lowest occurrences are:

1. Maryland (16.7 percent)
2. Pennsylvania (17.7 percent)
3. North Dakota (18.0 percent)
4. Illinois, Florida, and South Dakota (each with a rate of 18.1 percent)

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