Should adultery be a crime? It’s a felony in Idaho. - CSMonitor.com

When allegations erupted this summer that two Idaho lawmakers were caught in an extramarital affair, many supporters were quick to say their actions were a mistake, not a crime. However, in Idaho, adultery has been considered a felony since 1972. The crime is rarely prosecuted, but it remains on the books as a relic of America's long history of regulating sexual activity inside marriage....
http://www.csmonitor.com/USA/Justice/2016/0905/Should-adultery-be-a-crime-It-s-a-felony-in-Idaho