Spray CrockPot with cooking spray, or use a liner for easy clean up.
Add corn, Rotel, beans and diced onion to CrockPot and stir to combine.
In a small bowl, combine cream cheese, sour cream and milk; stir well.
Pour cream cheese mixture into CrockPot and stir to combine ingredients.
Sprinkle 1 cup of cheese over mixture.
Place lid on CrockPot and cook on LOW for 2 hours. When ready to serve, stir well and turn CrockPot to WARM. Add remaining 1/2 cup cheese over top of dip. Serve with your choice of chips.