Middletowntown (township), Newport county, southeastern Rhode Island, U.S., on Rhode (Aquidneck) Island, in Narragansett Bay. It was named for its location between the other two towns on the island, Newport and Portsmouth. Closely related to Newport, from which it was set off and incorporated in 1743, Middletown has developed as a residential suburb of that city. Middletown is the home of St. George’s School (1896) and the site of historic Whitehall (1729), built by Bishop George Berkeley, an Anglo-Irish philosopher who lived there from 1729 to 1731. The Norman Bird Sanctuary and Museum is nearby. Area 13 square miles (34 square km). Pop. (2000) 17,334; (2003 est.2010) 1716,359150.