JACKSON, Miss. (AP) — Most people in Mississippi’s county jails have been locked up at least three months while waiting to go on trial. Some have longer wait times because two-thirds of the counties only convene grand juries two or three times a year, according to a survey released Thursday by a group that tracks justice issues.

Mississippi does not require consistency among the 82 counties about how often grand juries meet to consider indictments — the formal charging documents to send a case to trial.

“If you get arrested in one of these counties where grand juries seldom meet, you can wind up in jail for months or even years just waiting to be indicted, and you will spend more time behind bars simply because of geographic misfortune,” said Cliff Johnson, an attorney who is director of the Roderick and Solange MacArthur Justice Center at the University of Mississippi School of Law.

Starting during the summer, law students and staff at the center spent several weeks issuing more than 100 public records requests and calling the offices of district attorneys and court clerks to gather information about the frequency of grand jury sessions.

In releasing the survey results, Johnson said Mississippi should join most other states in limiting how long prosecutors can delay seeking indictments. Mississippi, Alabama, Massachusetts, Oklahoma, and Virginia are the only states with no time limit on how long a person can be jailed without being indicted, he said.

Johnson estimated the cost for a Mississippi county to convene a grand jury at less than $5,000.

The survey found nearly 5,400 people were in Mississippi’s county jails — although Johnson said the number could be higher because jail population is notoriously difficult to track. The survey also found 2,683 pretrial detainees had been jailed longer than 90 days, more than 1,100 had been jailed at least nine months, and 747 had been jailed more than a year.

Johnson said the incarceration numbers are based on the most recent information that counties provided. Rules of criminal procedure only require sheriffs to say how many people have been detained at least 90 days, though some sheriffs release complete numbers of how many people are jailed, he said.

Some people are in Mississippi jails to serve short-term misdemeanor sentences. Some are there after a civil commitment for mental health issues or substance use. Those awaiting indictment are there because a judge would not set bond, or the person could not afford to post the bond that was set.

“So this is the big challenge — thousands of Mississippians are in our county jails, but it’s very difficult to know who is there, why, whether they have been indicted, whether they have a lawyer, or when they are supposed to get out,” Johnson said. “It’s a black hole.”

Five counties reported that grand juries meet monthly, but those results come with asterisks. DeSoto and Jackson counties “usually” meet that often, while Rankin County reported its grand jury meets “nearly every month.” Forrest and Stone are the other counties that reported monthly meetings.

The state’s largest county, Hinds, has two judicial districts. A grand jury meets six times a year in the Jackson-based district and three times a year in the Raymond-based district.

Another large county, Harrison, said a grand jury meets three times a year in each of its two judicial districts in Biloxi and Gulfport.

Two counties in the Delta — Leflore and Sunflower — reported that grand juries meet “as needed.” Leflore, Sunflower and Washington counties are in the same circuit court district and have the same district attorney.