Preheat the oven to 425ºF. Line a baking sheet with parchment paper.
Place the chicken drumsticks in a large bowl and drizzle the cooking oil over top. Add the garlic powder, salt, and pepper, then toss until the chicken is evenly coated in oil and seasoning.
Place the chicken drumsticks on the prepared baking sheet and bake for 40-45 minutes, or until the internal temperature reaches 175ºF and the drumsticks are browned. Flip the drumsticks once, halfway through baking.
After baking, transfer the drumsticks to a clean bowl. Melt the butter and drizzle it over the drumsticks. Gently toss the drumsticks to coat. Sprinkle the ranch seasoning over top then toss to coat again. Serve hot!