But the I-Team has found many cases where that measure of safety falls thru the cracks, allowing child sex offenders to live even closer than the lax law permits. And sometimes, they just disappear.
There are nearly 18,000 child sex offenders registered in Illinois, according to the state police. They are required to provide personal information once a year and have a new picture taken.
If what the I-Team found in just two days of looking through public records, checking apartment buildings, knocking on doors and measuring sidewalk then numerous child sex offenders are not where they claim to be; nor are they living within the law.
"There are so many examples of where the law is being violated that something needs to be done there," said State Rep. Darlene Senger.
In many states, residency laws prohibit child sex offenders from living within 2000 feet of a school. Most other states have at least a 1000-foot limit.
Illinois puts it at only 500 feet. But in a simply random check of child sex offenders, we found even that lenient limit can go unenforced.
Consider the case of Mung Lam, convicted of assaulting a 12 year old. The police consider Lam fully "compliant" by residing here in the Windale Hotel in Edgewater.
But there are two problems. First, the Windale is less than 500 feet from Swift Elementary School. Second, Lam doesn't even live there, according to the manager who introduced us to the occupant of the apartment Lam provided to police.
"We don't allow in murderers, child molesters or arsonists. They do a credit check," said Chris Hompton, building manager.
In Chicago's North Center neighborhood where students are already back to school at St. Benedict's, child sex offender Eric Dominguez lives in this building just down the street. According to a measurement, the apartment is slightly less than 500 feet from the intersection where the school is located. But the police record shows Mr. Dominguez is compliant with the law.
A Chicago police spokesman says they check distances by using a "web mapping system." Also, Chicago patrol units are said to check sex offender residences at least once a year as required by state law with detectives following up on apparent violators.
A head start preschool program is right around the corner from a home on West Erie St. It is the address listed on the registration for Jose Valentin whose victim was 10 years old, according to police records.
Authorities list him as "compliant" even though the preschool is less than 300 feet away. Police have given him until the middle of this month to move. Valentin's wife says her husband has already left.
Finally, there is Walter Pokatiloff who sexually abused a Lake County 6-year-old in 1991 and still has to register because of numerous probation violations.
Pokatiloff says he was living too close to a school but had to move.
"I had to move from another apartment building. I can't tell you which one but I had to move from there," said Pokatiloff.
And since he moved, Pokatiloff is now compliant, according to our measurement, by 55 feet.
During the past 2 years, Illinois legislators have voted down attempts to increase the distance to a thousand feet or more.
"Those who really want to commit crimes are going to commit crimes, it has nothing to do with, how, if they're within the 500 feet or 2000 feet or whatever. They could be within legal boundaries, but if there intent is to hurt again, they're going to do that," said State Rep. Darlene Senger, (R) Naperville.
Representative Senger has pushed to close the loopholes in Illinois' sex offender laws, acknowledging that the registry is not a cure-all.
Chicago police say their officers do personal address checks on registered sex offenders once a year. But as we found, even that isn't foolproof.
Illinois State Police Sex Offender Registry
Chicago Police Department Sex Offender Registry
Illinois Sex Offender Registry Team