Chaplin is accused of selling the drugs to an Appleton-area woman in May of 2017. She later died from the drugs.
Chaplin had bought the drugs from his supplier in Oshkosh, according to court documents. Law enforcement has linked that supplier's batch of fentanyl to at least four other overdose deaths in the Fox Valley. The investigation into those deaths continue.
Fentanyl is an opioid estimated to be 50 to 100 times more powerful than morphine.
The charge Chaplin pleaded guilty to has a mandatory sentence of 20 years in prison and up to a life sentence.