Place the bacon in a large Dutch oven and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain the bacon slices on a paper towel-lined plate, crumble and reserve for topping.
Cook and stir the onions and celery in the bacon drippings until tender, 5 to 10 minutes. Add chicken broth and potatoes, and bring to a boil over high heat. Reduce heat to medium-low and simmer until potatoes are fork-tender. Remove from heat and mash about 1/3 of the potatoes.
In a large bowl, combine flour and dry ranch mix. Whisk in the half-and-half and sour cream, beating well to combine thoroughly. Slowly whisk the sour cream mixture into the soup. Gently heat soup over medium heat to warm, do not boil. Season the soup with salt and pepper. To serve, top each bowl of soup with a sprinkle of bacon crumbles, Cheddar cheese and green onion.