The database shows that it is a P25 Phase 2 system. The Yankton PD talkgroups are currently Phase 1 and are not encrypted. Radio techs are Phase 2 and open also. I have no info about what will happen in the future. What scanner are your using? Hopefully, someone in your area has more info what is planned for the system. Yankton Police Trunking System, Yankton, South Dakota - Scanner Frequencies (radioreference.com)