Seion Congregational Chapel was built in 1788, rebuilt in 1821 and rebuilt again in 1873. The present chapel, dated 1873, is built in the Sub-Classical style with a gable-entry plan, by architect Evan Thomas. Seion has a symmetrical front facade and a central round-headed entrance with panelled double door and a glazed fanlight over. To either side is a tall, narrow, round-headed window with fixed glazing of 12-panes and a keystone. Also a central three light window of similar style over the door. At eaves level is a moulded roundel, with a circular opening in the apex of the gable. Quoins to each corner. Each side elevation has four full height windows identical to those on the front elevation, with the right side elevation also having a single width, round-headed doorway with panelled door. Seion closed during the late twentieth century and has since been converted into a dwelling, but the building is now Grade 2 Listed as a chapel of definite quality and character well restored as a house.

RCAHMW, February 2010