Preheat the oven to 400°F and lightly grease a large baking dish or sheet pan.
Arrange the chicken thighs in the dish, skin-side up. Scatter the halved baby potatoes evenly around and between the chicken thighs.
Drizzle the chicken and potatoes with olive oil, then sprinkle the ranch seasoning evenly over everything, making sure the chicken skin and potatoes are well coated.
Place the baking dish in the oven and bake for 40–45 minutes, or until the chicken reaches an internal temperature of 165°F and the potatoes are tender.
If desired, switch the oven to broil and cook for an additional 2–3 minutes to further crisp the chicken skin, watching closely.
Remove from the oven and let rest for 5 minutes before serving.
Pat the chicken dry first: Dry skin helps the chicken brown better and keeps it from steaming as it bakes.
Season after arranging: Sprinkling the ranch seasoning over the chicken and potatoes once they’re in the dish ensures even coverage and matches the one-pan method shown.
Keep the chicken skin-side up: This allows the fat to render as it cooks, helping the skin turn crisp while the meat stays juicy.
Don’t overcrowd the pan: Leave a little space between the chicken thighs and potatoes so everything roasts instead of steams.
Use broil carefully: A short broil at the end can boost crispiness, but watch closely to prevent burning.