William Chauncy Langdon (1831–1895) was a Protestant Episcopal clergyman and a prominent American proponent of the YMCA.
He founded three Episcopal Churches in Europe: Grace Church in Rome, 1859 (later renamed as St. Paul's Within the Walls); St James's in Florence, c. 1870; and Emmanuel_Episcopal_Church_(Geneva), 1873. These are now parishes of the Convocation of Episcopal Churches in Europe.
His son by the same name (1871–1947) was an historian of pageants.