The pipe organ is the best preserved product of the renowned Boston craftsman Thomas Appleton. Built in 1830, perhaps for South Church in Hartford, Connecticut, it was reinstalled by Emmons Howard in 1833 at Sacred Heart Church in Plains, Pennsylvania, where it was discovered, unused and neglected, in 1980. The organ's conservative tonal design and mahogany Greek Revival case reflect British models of the late eighteenth century. Standing more than fifteen feet high and having gold-leafed façade pipes (diapasons), the organ comprises sixteen ranks totaling 836 pipes, two 58-tone manuals, and a 27-note pedalboard, the latter replacing the shorter original one. Wind is supplied by hand-pumped bellows. The pipes of the upper manual are mainly enclosed in an elevated box with louvers that can be opened by a pedal for dynamic expression. The rest of the manual pipes are disposed above the recessed console, while the blowing apparatus and the key and stop mechanisms occupy the lower part of the case. The pedal rank rests on a separate wind chest behind the case. Tuning is in a customary mean tone temperament pitched at A=435.7 Hz.
Appleton's carving and joinery are particularly skillful. Before being hired by the prominent organ builder William Goodrich in 1807, Appleton had served an apprenticeship with the cabinetmaker Elisha Larned. Following a partnership with the piano makers Hayt and Alpheus Babcock, Appleton opened his own shop in 1820. In 1839 the Massachusetts Charitable Mechanic Association awarded him a gold medal, and his reputation continued to grow until he retired in 1869, by which time his numerous instruments were serving churches as distant as California and South Carolina.