This story was originally published by ProPublica Illinois.

Over the last 25 years, Illinois State Police have built a database of more than 90,000 people they deem to be gang members — but won’t say what gangs they’re in or where they live.

The Cook County sheriff’s office has a gang database, too. It includes 25,000 people, including hundreds whose gangs aren’t known and hundreds who are dead.

And the Illinois Department of Corrections says the only information it can provide about its gang database is that it can’t provide any information.

The Chicago Police Department’s massive gang database has received considerable scrutiny in recent months. But it’s not the only gang tracking system used by area law enforcement. Police and other authorities have been keeping files of alleged gang members for decades now. A Chicago officer recently told me that when he first joined the force in the 1980s, police bought high school yearbooks to help them keep track of names and faces in their districts.

Nowadays, the databases maintained by law enforcement are far bigger, more efficient and easier to share. But most still include information that’s subjective, unverified or simply wrong — though officials at hundreds of government agencies, and even some private institutions, can access and use them, with potentially troubling consequences.

Some of the mistakes are so obvious as to be absurd. The Chicago Police Department’s gang database included 13 people who were supposedly 118 years old, as I reported in April. Two others were listed as 132.

In response, the department promised to limit outside access to the database while allowing people listed in it to challenge the information. A police spokesman told me they’re still working on the changes. But last month four Chicago men filed a federal civil rights lawsuit alleging that false information in the database led to them being harassed by police, losing out on jobs and, in one case, facing deportation proceedings.

The databases maintained by the state police, the sheriff’s office and the Department of Corrections raise another round of questions about the fairness and accuracy of lists kept secret from the public but circulated widely among government officials.

Illinois State Police

The state police have refused to release copies of what officials call its “gang file,” denying multiple requests I submitted under the state’s Freedom of Information Act. Police officials said only authorized agencies are allowed to access the information, known as Law Enforcement Agencies Data System, or LEADS, which includes the gang database.

The state police eventually provided some figures that offer a glimpse of its gang records, but they raise as many questions as they answer.

As of July, more than 90,000 people are in the gang database, the state police said.

They were added not just by state troopers — more than 1,500 police departments, correctional facilities and other law enforcement agencies also have access to the database. In fact, two-thirds of the people in the database were entered by officials at county jails and state prisons, according to state police officials and records.

The other 31,000 were added by state police and local departments. A file provided by the state police shows that the biggest group was put into the system in the 1990s. Almost half are listed as white — though that also includes Hispanics.

The file is missing plenty of other important details. “We do not collect an ‘age’ data set,” a state police official wrote me. “We are also unable to provide data on ‘gang affiliation’ or ‘where the individual was first entered,’ nor are we able to provide the ‘reason the individual was entered’ because that is not included in our data sets.”

All gang information must be “corroborated by specific, documented and reliable information” that’s updated each year, said Lt. Matt Boerwinkle, a state police spokesman.

But what qualifies as “evidence” of gang membership is often open to interpretation. As with Chicago’s database, tattoos, emblems or other gang markings may count. In other cases, someone could be named as a gang member by a source who, according to police, has been “reliable” in the past.

Police officials said they work to make sure the database isn’t misused.

But records show the list of agencies that can access and use the information includes court systems, U.S. Customs and Immigration Enforcement, and investigative offices at the Chicago Housing Authority, the Illinois Tollway and the U.S. Fish and Wildlife Service. Even some private-sector institutions, such as the public safety department at the Moody Bible Institute, can get into the database.

In other words, the state police gang data potentially could surface in immigration enforcement, court proceedings, public housing investigations and campus policing — whether it’s accurate or not.

Cook County Sheriff

Chicago police officers have told me they’ve found the gang data tracked by the sheriff and the Department of Corrections to be more reliable than what’s in their own system. Their reasoning: When someone is locked up in the county jail or a state prison, he’s more likely to be truthful about his gang ties so he’s not housed in a dangerous situation with gang rivals.

But only some of the information maintained by the sheriff’s office comes from the jail. Authorities from 371 different agencies in Illinois, Indiana and Wisconsin can obtain or add information to what’s known formally as the Regional Gang Intelligence Database.

Jail officials said they ask about gang affiliations when they interview new inmates during intake. The information is then regularly updated. After a fight, for example, gang intelligence officers question inmates to determine what happened.

“They’ll take that information and put it into the databases for use out on the streets,” a veteran correctional officer at the jail told me. “Information actually flows both ways, from the streets back into the jail as well.”

Sheriff’s officials said the database follows federal guidelines for determining gang membership, which are similar to the state’s rules. A person must meet two of five qualifying indicators, a supervisor must approve the entry and the information has to be supported by documents.

Still, these determinations can be subjective. And even information that’s solid could soon be out of date. As the correctional officer pointed out to me, people often shift gang alliances or factions, making the data difficult to keep current.

In late June, the sheriff’s office provided me with a copy of the database in response to a Freedom of Information Act request.

The database includes more than 25,000 individuals. But sheriff’s officials also indicated that they maintain more data than they shared with me.

While entries are updated or “purged” after five years, the old data isn’t deleted altogether. If someone is later arrested or jailed again, authorities can “re-activate” the entry.

In some cases, key details appear to be missing from the copy I received. For example, more than 400 gangs and factions are listed in the data. They include large, well-known organizations such as the Gangster Disciples and Latin Kings but also more than 100 gangs that have only one listed member.

But more than 150 others are in the database even though their gangs are listed as “unknown” or “null.”

The database also includes more than 400 people who are unlikely to go back to the jail again, since they’re listed as dead.

Sheriff’s officials said such information can still help them prevent conflicts and investigate crimes. They stressed that the database does not provide probable cause to pull someone over or target them, acknowledging broader concerns over how law enforcement databases have been used. This week they even invited me to their offices to discuss them.

“We’re sensitive to the debate and concerned about it,” said Cara Smith, chief policy officer in the sheriff’s office. “We want to make sure the data we have is accurate and follows federal rules. But it also helps to ensure the safety and security of the jail.”

Illinois Department of Corrections

Police officers say the gang data maintained by IDOC is even better than what they get out of the jail. But state corrections officials will not answer even basic questions about how the information is collected, verified or used.

“IDOC tracks all gangs in the state of Illinois,” spokeswoman Lindsey Hess wrote in an email. “No further information can be released.”

The department’s secrecy is encoded in state law. In 2000, the General Assembly passed legislation formally creating a gang intelligence unit within the prison system. Information gathered by the unit “shall be highly confidential” and is not covered by the Freedom of Information Act.

However, the data “may be shared with other law enforcement agencies in order to curb gang activities outside of correctional institutions,” the law says.

When I asked for a list of how many agencies have access to its gang data, a department official responded: “IDOC does not maintain or possess records responsive to your request.”

So the Illinois Department of Corrections doesn’t know who else can see its gang database? The department won’t say.

State Sen. Patricia Van Pelt said these kinds of questions show why she has called for more oversight of gang databases. A bill she sponsored would prohibit their use outside law enforcement, but it’s been sitting in a House committee since passing the Senate in May.

In the meantime, as the result of a separate measure she pushed, state officials are required to conduct a review of gang databases and issue a report by January.

Van Pelt said that was the only way she could ensure the state agencies disclosed how the databases are being used.

“It’s so hard to get anything from them,” she said.