Keystone is an unincorporated community in Chester Township, Wells County, in the U.S. state of Indiana.A large share of the early settlers being natives of Pennsylvania caused the name of Keystone to be selected, after the Keystone State.A post office was established at Keystone in 1871, and remained in operation until it was discontinued in 1957.Keystone is located at 40°35′44″N 85°15′34″W / 40.59556°N 85.25944°W / 40.59556; -85.25944.