In a large bowl, combine potatoes, onion, soup, and cheddar cheese. Stir to combine.
Place the mixture in a lightly greased slow cooker.
Place cream cheese, butter, and salt & pepper on top of potato mixture.
Cook on low for 4-6 hours, stirring occasionally (I never stir more than once per hour). 4 hours will give you a slightly more runny and gooey Crockpot Cheesy Hashbrown Casserole, as pictured. 6 hours will give you a slightly more crispy dish.