Pierce Butler was Catholic.
Pierce Butler should not be confused with the similarly named 18th Century American politician Pierce Butler (a signer of the U.S. Constitution and a U.S. Senator in the First Federal Congress).
From: Jerry Filteau, "Alito would be fifth Catholic on Supreme Court", posted on Catholic News Service website, 31 October 2005 (http://www.catholicnews.com/data/stories/cns/0506179.htm; viewed 31 October 2005):
Past Catholics on the Supreme Court included... Joseph McKenna, Pierce Butler, Frank Murphy and William Brennan Jr.