Preheat oven to 400℉. Grease a 3-quart casserole dish.
Bring a large pot of lightly salted water to a boil. Add elbow macaroni and cook according to package directions until al dente; drain.
In a 3 quart saucepan over medium heat, melt butter and stir in flour. Cook for 1-2 minutes. Add milk gradually, whisking smooth after each addition. Bring to a simmer, stirring occasionally, and cook for 2-3 minutes or until thickened.
Turn heat off and stir in cream cheese, 2 cups of cheese and the ranch seasoning. Stir until cheese has melted and sauce is creamy. Add the cooked macaroni, chicken and half the bacon to the sauce.
Pour the mixture into the prepared dish. Top with remaining cheese and bacon crumbles. Bake for 15-20 minutes or until cheese is melted and bubbly.
Notes
Leftovers will keep in the refrigerator for 3 days and in the freezer for 4 weeks.