Around 1877, M.P. Moller began manufacturing pipe organs in Greencastle; and, he placed one in the German Reformed Church. This was one of the first M.P. Moller organs to be placed in any church anywhere. In January 1880, a committee was appointed to solicit funds for the purchase of the pipe organ at a price not to exceed four hundred twenty five dollars ($425.00). This new organ replaced the reed organ that had been in use. The pipe organ remained in the church and was used until it was replaced by a newer Moller instrument in 1902.
In 1902 it was brought to the attention of the consistory that the church organ was no longer satisfactory. Andrew Carnegie had agreed to contribute one half of the two thousand dollars ($2,000.00) required to purchase the new M.P. Moller pipe organ, after the congregation had raised the first one thousand dollars. A new pipe organ was installed in 1903. The first public recital was given on July 9; and, Miss Lore Brenisholtz was the church organist.
In 1951 the consistory of the church realized that the organ required extensive repairs. The congregation voted in 1951 to have a new organ installed by the M.P. Moller Company of Hagerstown, Maryland. The two manual pipe organ, installed at a cost of $10, 727.00, was dedicated on November 9, 1953.
In 2007 the Alsip-Lawson Memorial Organ Fund was established. With monies collected from this ongoing fund, an oboe stop was added to the 1953 Moller pipe organ in 2008. The pipes were manufactured by the former Eastern Organ Pipes, Inc. in Hagerstown, Maryland and were installed by Lawless-Johnson Organ Company in Greencastle, Pennsylvania. On September 14, the oboe stop and pipes were dedicated; and, a recital was given by the organist, Susan M. Alsip-Lawson.