Terry and Karen Obitts bought the building eight years ago.
"We knew there was a cornerstone but we figured it was probably empty," said Karen Obitts.
She credits her younger son, Drew, 13, with starting the ball rolling to open the stone.
"He got excited about the Civil War and wondered if there might be something in the stone that would be of interest," she said.
Drew ran into family friend Bill Showalter at church on Oct. 26 and asked him if he would open the cornerstone, which he did on Monday.
The cornerstone was laid on Sept. 10, 1870, in a ceremony marked by music, ritual and celebration.
Eureka Lodge No. 105 and the Orders of Red Men, Rechabites and Odd Fellows were major participants in the dedication ceremony, according to the "programme of ceremonies."
As the stone was carried to its resting place, Jacob Entler of Shepherdstown, W.Va., the master of ceremonies, asked each man to swear that his tools - the square, the level and the plumb - were true when they were used to make the stone.
Corn was cast over the stone to bless all who labor, wine was poured over the stone to ensure plenty, and oil was added so God would bless the congregation and preserve the peace.
The statement of beliefs contained in the box was signed by Elder Samuel Spurrier, preacher in charge; Samuel Boyer, Jonas Spielman, Elias Eakle, Henry Loman and Jacob Emmert, building committee and trustees.
"That box was soldered shut but it had rusted along one side," said Terry Obitts. "It's amazing to think how they made that hole in the concrete so precisely in those days with no power tools."
Terry Obitts said he has been poring over the nine-column newspapers from 1870, noting the changes in time and custom in 127 years.
Karen Obitts said she plans to contact Doug Bast, a Boonsboro historian, for advice on what to do with the artifacts.
"They need to be preserved," she said, marveling at the care parishioners took so many years ago.