According to the 2019 National Survey on Drug Use and Health, in 2019 an estimated 13.1 million adults had serious mental illness (SMI) in the past year. 34.5% of these individuals did not receive any treatment.
The most common reasons that individuals do not receive treatment include that they are not able to afford the cost, they thought that they could handle their condition without treatment, and they did not have time.
Substance Abuse and Mental Health Services Administration. (2020). Key substance use and mental health indicators in the United States: Results from the 2019 National Survey on Drug Use and Health (HHS Publication No. PEP20-07-01-001, NSDUH Series H-55). Rockville, MD: Center for Behavioral Health Statistics and Quality, Substance Abuse and Mental Health Services Administration.