Mercersburg's German Reformed congregation was founded in 1792. They led the effort to bring York's German Reformed seminary to Mercersburg in 1837; it moved to Lancaster in 1871 (LA25). Trinity Church is something of a fusion design, merging the dated classical style, here a pair of columns in antis within a portico that recalls William Strickland's St. John's Episcopal Church (1815–1816) at N. American and Brown streets in Philadelphia's Northern Liberties, with Gothic arches over the windows that attest to the new taste. The second-story sanctuary and mean interior stairs were inserted later.