Officers arrested a 43-year-old man in January in connection with a series of sexual assaults between 2003 and 2015.
Michael Bradley Hurst was charged with six counts of sexual assault and six counts of committing an indecent act.
On Friday, OPP announced 10 more charges of sexual assault had been laid against Hurst for a total of 22 sex-related offences.
Police added that investigators think there could still be more victims.
Anyone with information is urged to call 1-888-310-1122. Anonymous tips can be left with Crime Stoppers at 1-800-222-8477.
Palmerston is a small community with under 3,000 people in the town of Minto, approximately 60 kilometres northwest of Guelph.
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