First, check out what the crime he comitted.

I believe you can find more info from familywatchdog or local police officer. (If a 19yr old boy slept with his 17yr old girlfriend, he could still be convicted. However, he really is not harmful to public.) If his crime is targeting young child, or violence involved, you should think about moving yourself. (You can also talk to your local city/police department to see if there is restriction of sex offender cannot live with 500 ft within a school or daycare or something like that.)