The William E. Ward House, known locally as Ward's Castle, is located on Magnolia Drive, on the state line between Rye Brook, New York and Greenwich, Connecticut, United States. It is a reinforced concrete structure built in the 1870s. Ward, a mechanical engineer, built the house with his friend Robert Mook to demonstrate the viability of the material for building. It is the first reinforced concrete building in the United States. It was later purchased by Mort Walker, creator of the comic strip Beetle Bailey, who opened it as the Museum of Cartoon Art until 1992.