A 62-year-old St.Marys woman has been charged with murder.
Perth County OPP say they commenced an investigation on Wednesday into a death that happened in the area in 1985.
The victim has been identified as Meghan Thompson who was 25 days old at the time of her death.
Katherine Thompson has now been charged with first-degree murder and she was held in custody pending a bail hearing.
Police say this is an ongoing investigation and no further details will be released at this time.
A publication ban is in place for the proceedings.