Preheat oven to 350 degrees F. Spray a 9x13 baking dish with cooking spray.
In a large bowl, mix together the shredded chicken, sour cream, ranch seasoning, condensed chicken soup and buffalo sauce until well combined. Spread the chicken mixture evenly into the bottom of your baking dish.
Sprinkle the shredded cheddar cheese over the chicken mixture. Line the top of the casserole with frozen tater tots. Place the baking dish into the preheated oven and bake for 40 minutes, or until the chicken is cooked through and the tater tots are cooked and slightly browned and crispy.
Garnish the top of the casserole with the diced celery and serve immediately. Enjoy!
This casserole can be assembled a day ahead and refrigerated overnight.