Rockwood Hall was a Gilded Age mansion in Mount Pleasant, New York, on the Hudson River. It was best-known as the home of William Rockefeller, brother of John D. Rockefeller. Both brothers were co-founders of the Standard Oil Company. Other owners of the house or property included Alexander Slidell MacKenzie, William Henry Aspinwall, and Lloyd Aspinwall. The property was once up to 1,000 acres (400 ha) in size; the mansion at its height had 204 rooms, making it the second-largest private house in the U.S. at the time, only behind the Biltmore mansion in North Carolina. The estate is currently an 88-acre (36 ha) section of the Rockefeller State Park Preserve.