Karsten Koch, 34, has been living with his parents in Nashotah, but he would like to move out to his own place in Hartland to be closer to his job but not too far from family.
Hartland's police chief has warned Koch he's not welcome, citing the village's moratorium on any more sex offenders living there.
In a federal lawsuit, Koch contends that the village's 2018 ordinance, applied retroactively, amounts to an illegal ex post facto law, in violation of the U.S. Constitution.
The "designated offenders" banned by the ordinance include anyone on the state's sex offender registry. Koch is listed there because of a 2007 conviction for sexual assault of a child.