Welcome to 21055 Stonybrook Rd, Walnut, CA 91789 - a rare private estate located in one of Walnut's most desirable neighborhoods and served by the highly acclaimed Westhoff Elementary School in the award-winning Walnut Valley Unified School District. This beautifully upgraded home features 4 spacious bedrooms, 3 bathrooms, and an enormous bonus playroom perfect for a game room, home theater, gym, or children's entertainment space. Thoughtfully updated throughout, the home offers both comfort and functionality with an ideal layout for modern living and entertaining. Situated behind gates for added privacy and security, the property welcomes you with a long private driveway leading to the home, creating a peaceful estate-like setting. Nestled on an expansive 1.07-acre lot, this exceptional property offers incredible space and future potential, including room for an ADU or guest house. The resort-style backyard is truly an entertainer's dream, featuring a large sparkling pool and spa surrounded by mature landscaping and open space. Whether hosting gatherings, relaxing with family, or enjoying the serene setting, this backyard offers endless possibilities for indoor-outdoor California living. Rarely does a property combine privacy, acreage, luxury amenities, top-rated schools, and future expansion potential all in one exceptional offering. Conveniently located near parks, shopping, dining, and easy freeway access, this Walnut gem truly has it all. Don't miss this extraordinary opportunity to own a private estate in the heart of Walnut!