Understanding Trends in Jail Population in St. Louis County, Missouri: 2010 – 2019

This report and related research brief provide key metrics on the jail population in St. Louis County, Missouri, including trends in jail admissions, length of stay, bed days utilized, and individuals who return to jail repeatedly. These reports provide insights into the factors driving jail populations in LMDC and highlights policy changes that may be influencing the number of people admitted to jail and how long they stay in jail. This study was funded by the Pew Charitable Trusts and is the first in a series of studies on jail populations in jurisdictions that make up The Research Network on Misdemeanor Justice (RNMJ), a project of the Data Collaborative for Justice (DCJ). 

Key Findings:

  • Fewer arrests for misdemeanors, violations, victimless non-violent charges (e.g., drug use and possession) and traffic offenses are driving decreases in the number of people admitted to jail. From 2010 to 2019, annual admissions to DJS decreased by 40%, from a high of 33,976 admissions to a low of 20,216.
  • Increases in length of stay are a key driver of jail populations. The average length of stay rose from 14.9 days in 2010 to a high of 26.4 days in 2018, a 77% increase. It then declined to 23.3 days in 2019, when it was 56% longer than in 2010.
  • People under probation supervision make up a significant portion of jail populations. While the group’s average length of stay declined from 40.7 days in 2010 to 30.4 days in 2019, individuals who entered jail for only a probation violation had the second-longest length of stay over most of the study period. The only group with a longer average length of stay was people booked into jail on a sentence for a city or county conviction.
  • Bail continues to be a key driver of jail populations. In 2010, 259,751 bed days were occupied by individuals with bail amounts over $5,000, which is 49% of all bed days used in that year. In 2019, this number rose to 361,175, or 70% of all bed days.
  • Black people are disproportionately represented in jail admissions and experienced significant increases in lengths of stay between 2010 and 2019. In 2019, 25% of St. Louis County residents identified as Black, but Black people accounted for 55% of admissions and 67% of bed days. In 2019, Black people stayed in jail an average of 12 days longer than white people.
  • Understanding people who are frequently re-admitted to jail may help reduce jail populations. Of individuals released from jail in 2010, 58% were readmitted by 2019; 40% returned more than once and 15% were readmitted 5+ times.