About 30% of state and federal prisoners and 40% of local jail inmates reported having at least one disability in 2011-12, according to the most recent report on the subject from the U.S. Bureau of Justice Statistics. In the same years, 11% of people in the general population reported having some kind of disability. The report said 19.5% of state and federal prisoners reported a cognitive disability, the most common disability cited, compared with 4.8% of the general population.
According to the Center for American Progress, a left-leaning think tank, the disproportionate number of disabled people behind bars is in part a result of mental-health policy changes in the latter half of the 20th century. Hundreds of thousands of mentally disabled individuals were released from large institutions without adequate investment in alternative housing and support. Many ended up in the prison system.