Combine all ingredients in a 5- or 6-quart slow cooker. Cover and cook on HIGH 18 hours or until peanuts are soft. Drain peanuts before serving or storing. Store in zip-top plastic bags in refrigerator up to 2 weeks.
Cajun Boiled Peanuts: Add 1 (3-ounce) package boil-in-bag shrimp and crab boil and 1/3 to 1/2 cup hot sauce (we tested with Frank's) to slow cooker before cooking.
Freeze It!: Freeze these peanuts in zip-top freezer bags up to 2 months. Reheat them in the microwave before serving.