Old South Church in Boston, Massachusetts, is a historic United Church of Christ congregation first organized in 1669. Its present building was designed in the Gothic Revival style by Charles Amos Cummings and Willard T. Sears, completed in 1873, and amplified by the architects Allen & Collens between 1935–1937. The church, which was built on newly filled land in the Back Bay section of Boston, is located at 645 Boylston Street on Copley Square.