On the heels of chicagocrime.org et al., Harper Reed has created a mapping application that locates sex offenders in Chicago who are registered with the Illinois State Police. He encourages you to read the ISP's disclaimer, which, paraphrased, warns that the information is historical, makes no claims about possible recidivism, and should not be used to harass, threaten, etc. (I point that out because, well, I grappled for a long while with whether it was right to post this at all.)