What Drives the Jail Population

There are two main types of admissions to the jurisdiction of the Cook County Sheriff’s Office:

1. Confinement in jail
2. Supervision in the community (for example, electronic monitoring)

The total number of admissions to jurisdiction of the Sherriff’s Office, both confinement and community supervision, has dropped by almost half between 2008 and 2017.

The average daily population confined in jail has also declined (down 24%), although not as steeply as annual admissions (down 49%).

The total average daily population, including people in jail and those in electronic monitoring programs, has only dropped 9%, while the electronic monitoring (EM) program has grown substantially by 234%. The biggest jump took place after 2011, when the Sheriff’s Office expressly expanded the EM program.

Compared to those confined in jail, the percentage of people under the jurisdiction of the Sheriff’s Office who are in the electronic monitoring program has risen substantially—from 6% to 29%, while the confined population share of the total has dropped from 94% to 71%.

Meanwhile, the average length of time spent in jail by the shrinking jail population has become longer.

Another way to understand this is to note that In 2000, it took 10 admissions to jail a year to fill one jail bed for a year. By 2017, it only took 6.7 admissions to fill the same bed.

There are two ways this can happen:

1. There are fewer people facing low level cases entering the jail, resulting in a smaller jail population overall but a higher proportion of people facing serious cases. These cases take longer to adjudicate, thus raising the overall average time spent in jail (Compositional change).
2. The same kind of cases that took less time to prosecute in the past now take longer (Transactional change).

One reason total jail admissions are down is because the police are making fewer felony arrests. Not only has the overall volume of felony arrests gone down but the composition of charges faced by those arrestees has changed. Lower level felony arrests (class 3 or 4) have fallen more steeply (by 27%) than higher level felony arrests (class 1 or 2), which have fallen by 20%.

This gives some support to explaining the rise in the average length of stay in jail as a result of the diversion of less serious cases, such that the remaining jail population is on average composed of more serious cases.

Fewer felony arrests have led to a decline in felony case filings by the State’s Attorney’s Office (SAO). Felony filings have fallen by 29%, ten points less than felony arrests have fallen (39%); while misdemeanor filings have dropped even more sharply, by 46%.

The shallower drop in felony cases filings by SAO than in felony arrests by police, demonstrates the filtering role that SAO plays in determining which cases go to court, and adds further weight to the explanation that a change in the composition of the court bound population is resulting in an increase in the average length of stay of people in jail.

Between 2005 and 2014, the number of felony cases faced by the courts on one day has decreased, increased, and started to decrease again; resulting in an overall drop of 11%.

Were this overall trend to continue, it would give credence to the explanation that part of the increase in average length of stay in the jail is due to an increase in the time it’s taking in court to resolve some cases of the same type today than in the past.

Between 2002 and 2015, the average time it takes in court to resolve felony cases has increased 51%. If this substantial increase is due entirely or primarily to a reduction in the number of less serious cases filed with the Court, than theoretically, in the long run, the Court should begin to reduce the backlog of cases that it inherits from one year to the next.

The time it takes for half of all cases to be resolved through a plea of guilty has increased over the last six years by approximately 33%. For cases initiated in 2012, it took approximately six months for half to be resolved as guilty pleas. For cases initiated in 2016 it took about eight months.

Over that time, the mix of cases reaching a plea of guilty does not appear to have changed substantially, giving further credence to the explanation that at least in part, the time some types of cases have been treated in the court has changed.