"The trendline for state prisoner populations continues to slowly decline. According to the Bureau of Justice Statistics, states held 27,788 fewer prisoners at year-end 2019 than in 2018, a decline of 2.2 percent, and more than 143,700 less than in 2009, a decrease of 10.5 percent. Thirty-three states had a decrease in their sentenced prison population in 2019, while 13 states had increases. Even as the number of prisoners continues a gradual decrease, state spending on corrections has seen annual growth.
"While the number of prisoners is declining, states will not capture significant savings until the population is reduced enough to close a prison unit or facility, which decreases the number of staff needed. The primary cost drivers in corrections are personnel costs, care and support for inmates including health care, contract costs for community-based programs, and maintenance of a large physical plant. Related to these cost drivers, the mix of prisoners is also changing, with an increasing number of inmates aged 55 or older. In 2011, the percentage of sentenced prisoners under the jurisdiction of states and the federal government in this age group was 7.9 percent; by 2019, that number had risen to 13.1 percent. Having a larger percentage of older inmates often translates to increased health care costs as well as necessary facility changes to accommodate an aging population."
National Association of State Budget Officers (2020). 2020 State Expenditure Report: Fiscal Years 2018-2020.