Castlerock Homes Apartments for rent in Billings, MT on ForRent.com: (866) 898-9755 - Availability, pricing and special promotions subject to change daily. Located in beautiful northern Billings, on the cusp of the famous Rim Rock, Castlerock Apartment Homes offer quality living in one of the most picturesque settings of the city. The pool, hot-tub, and exercise room were all designed with your stress-free living in mind. And at Castlerock Apartment Homes, your pets are more than welcome.