It is unknown at this time from which year this originated.

Here is a description of the Church:

The Octoraro Methodist Episcopal Church was built early in the 18th Century to provide a place of worship to the nearby farmers. The name “Gray Horse Church” received its familiar but unofficial name for an old grey horse that was used to bring wood and materials from the mill for the builders to hoist into position. The Mason-Dixon Line runs through the structure, the pulpit being in Chester County, PA, the rest in Cecil County, MD. At one time, it was quite popular to hike up to the site of the Church and bring back a key from the old pump organ that was inside, just to prove that you had hiked all the way up the hill.